A battery open-circuit voltage temperature compensation measurement method and device based on bidirectional temperature scanning

Abstract

The application discloses a battery open-circuit voltage temperature compensation measurement method and device based on bidirectional temperature scanning, and relates to the technical field of battery open-circuit voltage estimation. The battery to be measured is placed in a starting temperature environment to obtain a first open-circuit voltage; the battery to be measured is adjusted to a terminal temperature to obtain a second open-circuit voltage; if a current expected voltage error is greater than a maximum voltage error threshold, state resetting is performed on the battery to be measured, the battery to be measured is placed at the terminal temperature to obtain a third open-circuit voltage, and the battery to be measured is adjusted to the starting temperature to obtain a fourth open-circuit voltage; and the first open-circuit voltage, the second open-circuit voltage, the third open-circuit voltage and the fourth open-circuit voltage are subjected to difference method calculation to obtain a self-discharge influence quantity and a temperature influence quantity. By means of the bidirectional temperature scanning strategy, the method effectively solves the problem that the temperature influence quantity and the self-discharge influence quantity cannot be separated in the prior art.

Description

Technical Field

[0001] This application relates to the field of battery open-circuit voltage estimation technology, specifically to a battery open-circuit voltage temperature compensation measurement method and device based on bidirectional temperature scanning. Background Technology

[0002] Open-circuit voltage (OCV) is a crucial state parameter for batteries, widely used in battery production processes such as sorting and grouping, and state of charge (SOC) estimation. Because battery OCV exhibits significant temperature dependence, its value changes with ambient temperature. Therefore, when measuring OCV at non-standard temperatures or comparing OCV values ​​measured at different temperatures, high-precision temperature compensation corrections must be performed to ensure the accuracy of battery state assessment and classification.

[0003] In existing technologies, a unidirectional temperature path testing method is typically used to obtain the influence coefficient of temperature on OCV. Specifically, this method involves placing the battery under test at a certain initial temperature for a sufficient time to reach thermal equilibrium, then measuring the initial OCV. Subsequently, the ambient temperature is unidirectionally increased or decreased to another termination temperature, and the battery is placed for the same amount of time again before measuring the final OCV. Finally, the temperature compensation coefficient of the battery is obtained by directly calculating the difference in OCV between the two measurements and dividing it by the temperature change.

[0004] However, the existing unidirectional temperature scanning method assumes that the change in OCV during the resting period is entirely caused by temperature changes, incorrectly attributing the voltage decay caused by self-discharge as part of the temperature effect. It cannot effectively separate the temperature effect from the self-discharge effect through mathematical calculations, and the final calculated temperature compensation coefficient actually incorporates the interference error from self-discharge, leading to distorted measurement results. Summary of the Invention

[0005] This application provides a method and apparatus for measuring the open-circuit voltage temperature compensation of a battery based on bidirectional temperature scanning. This method effectively solves the problem that the influence of temperature and the influence of self-discharge cannot be separated in the prior art through a bidirectional temperature scanning strategy.

[0006] In a first aspect, this application provides a method for measuring the open-circuit voltage temperature compensation of a battery based on bidirectional temperature scanning. The method includes: placing the battery under test in a preset state of charge in an environment at an initial temperature for a preset time, and measuring a first open-circuit voltage; adjusting the ambient temperature of the battery under test to a final temperature and placing it for a preset time, and measuring a second open-circuit voltage; acquiring the open-circuit voltage curve of the battery under test at a standard temperature, extracting the curve slope corresponding to the preset state of charge, and retrieving the hysteresis difference and high-temperature aging value corresponding to the material of the battery under test; calculating the curve slope, hysteresis difference, and high-temperature aging value to obtain the current expected voltage error; comparing the current expected voltage error with a maximum voltage error threshold; if the current expected voltage error is greater than the maximum voltage error threshold, resetting the state of the battery under test, and setting the reset battery under test to... The battery is left to stand at the termination temperature for a preset time, and the third open-circuit voltage is measured. The ambient temperature of the battery under test is then adjusted to the starting temperature and left to stand for a preset time, and the fourth open-circuit voltage is measured. The self-discharge effect and temperature effect of the battery under test are calculated by the difference method based on the first, second, third, and fourth open-circuit voltages. If the current expected voltage error is less than or equal to the maximum voltage error threshold, the battery under test is kept in continuous testing state, and it is left to stand at the termination temperature for a preset time to measure the fifth open-circuit voltage. The ambient temperature of the battery under test is then adjusted to the starting temperature and left to stand for a preset time to measure the sixth open-circuit voltage. The self-discharge effect and temperature effect of the battery under test are calculated by the slope averaging method based on the first, second, fifth, and sixth open-circuit voltages.

[0007] By adopting the above technical solution, at the beginning of the measurement, the battery under test is placed in an environment at the initial temperature under a preset state of charge for a preset time, and the first open-circuit voltage is measured. The ambient temperature is then adjusted to the termination temperature, and the battery is placed for the same amount of time to measure the second open-circuit voltage. This process constitutes the first temperature change path. By obtaining the open-circuit voltage curve of the battery under test at the standard temperature and extracting the slope of the curve corresponding to the preset state of charge, combined with the hysteresis difference and high-temperature aging value of the material, a comprehensive calculation is performed to pre-assess the current expected voltage error and compare it with the maximum voltage error threshold, thereby intelligently selecting the subsequent test path. When the current expected voltage error exceeds the maximum voltage error threshold, the battery under test is reset and a reverse temperature scan continues. The third and fourth open-circuit voltages are measured at the termination and start temperatures, respectively. Symmetrical calculations using the difference method effectively offset unidirectional cumulative errors such as self-discharge, thus accurately extracting the temperature effect. When the current expected voltage error is less than or equal to the maximum voltage error threshold, the battery under test remains in a continuous testing state. Only the fifth and sixth open-circuit voltages need to be measured at the termination and start temperatures. The self-discharge effect is estimated and corrected using the slope averaging method. This method eliminates the need for time-consuming state resets, significantly shortening the testing cycle and improving testing efficiency.

[0008] Optionally, the self-discharge effect and temperature effect of the battery under test can be calculated by the difference method for the first open-circuit voltage, the second open-circuit voltage, the third open-circuit voltage, and the fourth open-circuit voltage. Specifically, this includes: subtracting the second open-circuit voltage from the first open-circuit voltage to obtain the temperature rise voltage difference; subtracting the third open-circuit voltage from the fourth open-circuit voltage to obtain the temperature fall voltage difference; adding the temperature rise voltage difference and the temperature fall voltage difference and dividing by two to obtain the temperature effect of the battery under test; and subtracting the temperature fall voltage difference from the temperature rise voltage difference and dividing by two to obtain the self-discharge effect of the battery under test.

[0009] By adopting the above technical solution, during the bidirectional temperature scanning process, the heating voltage difference is obtained by subtracting the second open-circuit voltage from the first open-circuit voltage. This heating voltage difference includes both the voltage change caused by the temperature rise and the voltage drop caused by self-discharge during the resting period. After eliminating historical influences through state reset, the cooling voltage difference is obtained by subtracting the third open-circuit voltage from the fourth open-circuit voltage. This cooling voltage difference includes both the voltage change caused by the temperature drop and the voltage drop caused by self-discharge during the same resting period. Since the magnitude of the temperature change from the initial temperature to the final temperature is equal to the temperature change from the final temperature back to the initial temperature, and the direction is opposite... Conversely, the effect of temperature on open-circuit voltage exhibits opposite signs in the two measurements, while self-discharge, as a unidirectional cumulative process, consistently shows a voltage decrease with essentially the same degree of influence in both measurements. When the difference between the heating and cooling voltages is added together and then divided by two, the effects of self-discharge cancel each other out due to their identical signs, while the effects of temperature are amplified due to their opposite signs, thus accurately extracting the temperature influence of the battery under test. When the difference between the heating and cooling voltages is subtracted from the difference in heating voltage and then divided by two, the effects of temperature cancel each other out due to their opposite signs, while the effects of self-discharge become apparent due to their identical signs, thus accurately obtaining the self-discharge influence of the battery under test.

[0010] Optionally, the slope averaging method is used to calculate the self-discharge effect and temperature effect of the battery under test for the first, second, fifth, and sixth open-circuit voltages. Specifically, this includes: dividing the difference between the fifth and second open-circuit voltages by a first time interval to obtain an estimated value of the self-discharge coefficient in the high-temperature region, where the first time interval is the time interval between the fifth and second open-circuit voltages; and dividing the difference between the sixth and first open-circuit voltages by a second time interval to obtain an estimated value of the self-discharge coefficient in the low-temperature region, where the second time interval is the time interval between the sixth and first open-circuit voltages. The self-discharge coefficient estimates for the high-temperature region and the low-temperature region are averaged to obtain the self-discharge influence. Based on the self-discharge influence and the time parameters corresponding to each measurement, the target voltage deviation caused by self-discharge at each measurement point is calculated. The corresponding target voltage deviation is subtracted from the first open-circuit voltage, the second open-circuit voltage, the fifth open-circuit voltage, and the sixth open-circuit voltage for time correction to obtain multiple corrected open-circuit voltages. Based on the temperature difference between the starting temperature and the ending temperature, and the voltage difference between the corresponding corrected open-circuit voltages at different temperatures, the temperature influence of the battery under test is calculated.

[0011] By employing the above technical solution, the second and fifth open-circuit voltages measured during the continuous static period of the battery under test at the termination temperature are used. The difference between these two voltages is divided by the first time interval to obtain an estimated value of the self-discharge coefficient in the high-temperature region. Simultaneously, the first and sixth open-circuit voltages measured after the battery under test returns to the starting temperature are used. The difference between these two voltages is divided by the second time interval to obtain an estimated value of the self-discharge coefficient in the low-temperature region. Averaging the estimated values ​​of the self-discharge coefficients in the high-temperature and low-temperature regions yields a self-discharge influence quantity that comprehensively reflects the overall effect of self-discharge under different temperature conditions, avoiding the one-sidedness of measurements at a single temperature point. After obtaining the self-discharge influence quantity, the time parameters corresponding to each measurement are used... The target voltage deviation caused by self-discharge at each measurement point is calculated separately, and the corresponding target voltage deviation is subtracted from the first, second, fifth, and sixth open-circuit voltages for time correction. The multiple corrected open-circuit voltages obtained after time correction truly reflect the voltage change caused by pure temperature factors. Based on the temperature difference between the starting and ending temperatures, and the voltage difference between the corresponding corrected open-circuit voltages at different temperatures, the temperature influence of the battery under test is accurately calculated. Compared with the difference method, which requires a state reset operation, the slope averaging method maintains the continuous test state of the battery under test and avoids the time-consuming discharge and recharge process, significantly shortening the test cycle while ensuring measurement accuracy.

[0012] Optionally, based on the temperature difference between the starting temperature and the ending temperature, and the voltage difference between the corresponding corrected open-circuit voltages at different temperatures, the temperature influence of the battery under test is calculated. Specifically, this includes: calculating the first corrected voltage difference between the corrected open-circuit voltage corresponding to the second open-circuit voltage and the corrected open-circuit voltage corresponding to the first open-circuit voltage, and calculating the first temperature difference between the ending temperature and the starting temperature; using the ratio of the first corrected voltage difference to the first temperature difference as the temperature coefficient of the heating path; calculating the second corrected voltage difference between the corrected open-circuit voltage corresponding to the sixth open-circuit voltage and the corrected open-circuit voltage corresponding to the fifth open-circuit voltage, and calculating the second temperature difference between the starting temperature and the ending temperature; using the ratio of the second corrected voltage difference to the second temperature difference as the temperature coefficient of the cooling path; and averaging the temperature coefficients of the heating path and the cooling path to obtain the temperature influence.

[0013] By employing the above technical solution, the first corrected voltage difference between the corrected open-circuit voltage corresponding to the second open-circuit voltage and the corrected open-circuit voltage corresponding to the first open-circuit voltage is calculated. This difference accurately reflects the voltage change of the battery under test caused by pure temperature factors during the process of rising from the initial temperature to the final temperature. Combined with the temperature coefficient of the heating path calculated from the first temperature difference between the final temperature and the initial temperature, the change law of the open-circuit voltage with temperature in the temperature rise path of the battery can be accurately characterized. The second corrected voltage difference between the corrected open-circuit voltage corresponding to the sixth open-circuit voltage and the corrected open-circuit voltage corresponding to the fifth open-circuit voltage is also calculated. This difference accurately reflects the voltage change of the battery under test caused by pure temperature factors during the process of rising from the initial temperature to the final temperature. The voltage change caused by pure temperature factors during the process of the battery dropping from the termination temperature to the starting temperature, combined with the second temperature difference between the starting temperature and the termination temperature, is used to calculate the temperature coefficient of the cooling path. This can accurately characterize the change of the open-circuit voltage with temperature in the cooling path. Due to the hysteresis characteristics of the battery material and the influence of the temperature history on the internal electrochemical state, there may be slight differences between the temperature coefficients measured by the heating path and the cooling path. Averaging the temperature coefficients of the heating path and the cooling path can eliminate the random errors and directional deviations of single-path measurements, making the measurement results more stable and reliable.

[0014] Optionally, the curve slope, hysteresis difference, and high-temperature aging value are calculated to obtain the current expected voltage error. Specifically, this includes: obtaining the reversible self-discharge rate of the battery under test at the test temperature, the estimated time spent at the target temperature, and the hysteresis activation coefficient; adding the reversible self-discharge rate to the high-temperature aging value to obtain the total capacity loss rate, where the high-temperature aging value is the irreversible aging rate calculated based on the Arrhenius equation; multiplying the absolute values ​​of the total capacity loss rate, the estimated time, and the curve slope to obtain the first voltage error term; multiplying the hysteresis activation coefficient and the hysteresis difference to obtain the second voltage error term; and adding the first voltage error term and the second voltage error term to obtain the current expected voltage error.

[0015] By employing the above technical solution, key parameters such as the reversible self-discharge rate of the battery under test at the test temperature, the estimated time spent at the target temperature, and the hysteresis activation coefficient are obtained. The total capacity loss rate is obtained by adding the reversible self-discharge rate to the high-temperature aging value. The first voltage error term, calculated by multiplying the total capacity loss rate, the estimated time, and the absolute value of the curve slope, accurately quantifies the error contribution of capacity loss mapped to the voltage domain through the open-circuit voltage curve. The absolute value of the curve slope reflects the sensitivity of the voltage at different state of charge points to capacity changes. The second voltage error term, calculated by multiplying the hysteresis activation coefficient and the hysteresis difference, accurately quantifies the additional voltage deviation introduced by the temperature history activation hysteresis effect. The current expected voltage error, obtained by adding the first and second voltage error terms, comprehensively reflects the superimposed effect of the three mechanisms of self-discharge, aging, and hysteresis. By comparing with the maximum voltage error threshold, it is possible to determine in advance whether the difference method or the slope averaging method is more appropriate, thereby optimizing the test process while ensuring measurement accuracy and avoiding time waste or insufficient accuracy caused by blindly selecting a test scheme.

[0016] Optionally, the hysteresis activation coefficient of the battery under test is obtained, specifically including: obtaining the absolute temperature difference between the initial temperature and the target temperature; dividing the absolute temperature difference by the reference temperature span to obtain the temperature activation factor; obtaining the estimated time for the battery under test to stand at the target temperature, and dividing the estimated time by the hysteresis relaxation time constant to obtain the time ratio; calculating the power function value of the natural constant with the negative of the time ratio as the exponent, and subtracting the power function value from 1 to obtain the time relaxation factor; multiplying the temperature activation factor and the time relaxation factor to obtain the hysteresis activation coefficient.

[0017] By adopting the above technical solution, the absolute temperature difference between the initial temperature and the target temperature is obtained and divided by the reference temperature span to obtain the temperature activation factor. At the same time, the estimated time for the battery under test to stand at the target temperature is obtained and divided by the hysteresis relaxation time constant to obtain the time ratio. By calculating the power function value of the natural constant with the negative number of the time ratio as the exponent and subtracting the power function value from 1 to obtain the time relaxation factor, the dynamic evolution process of the hysteresis effect gradually developing and tending to saturate over time is accurately described. The hysteresis activation coefficient obtained by multiplying the temperature activation factor and the time relaxation factor comprehensively considers the two key dimensions of temperature drive and time evolution, which significantly improves the adaptability of the temperature compensation measurement method.

[0018] Optionally, the open-circuit voltage curve of the battery under test at a standard temperature is obtained, and the slope of the curve corresponding to the preset state of charge is extracted. Specifically, this includes: obtaining the first voltage and state of charge data of the battery under test during discharge at a standard temperature; charging the battery under test with a constant current until the charging cutoff condition is met, and obtaining the second voltage and state of charge data during the charging process; calculating the arithmetic mean of the first voltage and the second voltage under the same state of charge, and fitting the arithmetic mean corresponding to each state of charge point to generate the open-circuit voltage curve at the standard temperature; determining the target voltage point corresponding to the preset state of charge on the open-circuit voltage curve; selecting the first state of charge point and the second state of charge point within a preset neighborhood of the preset state of charge, and obtaining the first voltage value corresponding to the first state of charge point and the second voltage value corresponding to the second state of charge point from the open-circuit voltage curve respectively; dividing the difference between the first voltage value and the second voltage value by the difference between the first state of charge point and the second state of charge point to obtain the slope of the curve corresponding to the preset state of charge.

[0019] By employing the above technical solution, the first voltage and state of charge (SOC) data of the battery under test during discharge at a standard temperature are obtained. The battery is then charged at a constant current until the charging cutoff condition is met, and the second voltage and SOC data during the charging process are acquired. The arithmetic mean of the first and second voltages under the same SOC is calculated, effectively eliminating the influence of the inherent charge-discharge hysteresis effect of the battery material on the open-circuit voltage measurement. Compared to existing technologies that only use a single charge or discharge curve, this method can obtain an open-circuit voltage characteristic that more closely approximates the true thermodynamic equilibrium state. Furthermore, the open-circuit voltage curve at the standard temperature, fitted based on the arithmetic mean of each SOC point, truly reflects... This method reflects the intrinsic relationship between voltage and state of charge (SOC) of a battery under no-current polarization conditions. After determining the target voltage point corresponding to the preset SOC on the open-circuit voltage curve, a first SOC point and a second SOC point are selected within a preset neighborhood of the preset SOC, and the corresponding first and second voltage values ​​are obtained respectively. The slope of the curve obtained by dividing the difference between the first and second voltage values ​​by the difference between the first and second SOC points using the local difference method can accurately reflect the sensitivity of the voltage to capacity changes near the SOC. Local slope extraction can better capture the nonlinear characteristics of the open-circuit voltage curve in different SOC intervals.

[0020] A second aspect of this application provides a battery open-circuit voltage temperature compensation measurement device based on bidirectional temperature scanning. The device includes a first measurement unit, a processing unit, a second measurement unit, and a calculation unit. The first measurement unit places the battery under test in a preset state of charge at an initial temperature environment for a preset time and measures the first open-circuit voltage; then adjusts the ambient temperature of the battery under test to a final temperature and places it for a preset time, measuring the second open-circuit voltage. The processing unit acquires the open-circuit voltage curve of the battery under test at a standard temperature, extracts the curve slope corresponding to the preset state of charge, and retrieves the hysteresis difference and high-temperature aging value corresponding to the material of the battery under test; calculates the curve slope, hysteresis difference, and high-temperature aging value to obtain the current expected voltage error; and compares the current expected voltage error with a maximum voltage error threshold. The second measurement unit, if the current expected voltage error is greater than the maximum voltage error threshold, then... The battery is reset, and the reset battery under test is placed at the termination temperature and left to stand for a preset time. The third open-circuit voltage is measured. The ambient temperature of the battery under test is adjusted to the starting temperature and left to stand for a preset time. The fourth open-circuit voltage is measured. If the current expected voltage error is less than or equal to the maximum voltage error threshold, the battery under test is kept in continuous testing state. It is left to stand at the termination temperature for a preset time and the fifth open-circuit voltage is measured. The ambient temperature of the battery under test is adjusted to the starting temperature and left to stand for a preset time. The sixth open-circuit voltage is measured. The calculation unit calculates the self-discharge effect and temperature effect of the battery under test by using the difference method on the first, second, third, and fourth open-circuit voltages. The slope averaging method is used to calculate the self-discharge effect and temperature effect of the battery under test.

[0021] In a third aspect, this application provides an electronic device including a processor, a memory, a user interface, and a network interface. The memory is used to store instructions, the user interface and the network interface are used to communicate with other devices, and the processor is used to execute the instructions stored in the memory, causing the electronic device to perform any of the methods described above in this application.

[0022] In a fourth aspect, this application provides a computer-readable storage medium storing instructions that, when executed, perform any of the methods described above in this application.

[0023] In summary, one or more technical solutions provided in the embodiments of this application have at least the following technical effects or advantages: 1. At the beginning of the measurement, the battery under test is placed in an environment at the initial temperature under a preset state of charge for a preset time, and the first open-circuit voltage is measured. The ambient temperature is then adjusted to the termination temperature, and the battery is placed for the same amount of time to measure the second open-circuit voltage. This process constitutes the first temperature change path. By acquiring the open-circuit voltage curve of the battery under test at the standard temperature and extracting the slope of the curve corresponding to the preset state of charge, combined with the hysteresis difference and high-temperature aging value of the material, a comprehensive calculation is performed to pre-assess the current expected voltage error and compare it with the maximum voltage error threshold, thereby intelligently selecting the subsequent test path; the current expected... When the voltage error exceeds the maximum voltage error threshold, the battery under test is reset and a reverse temperature scan continues. The third and fourth open-circuit voltages are measured at the termination and start temperatures, respectively. Symmetrical calculations using the difference method effectively offset unidirectional cumulative errors such as self-discharge, thus accurately extracting the temperature effect. When the current expected voltage error is less than or equal to the maximum voltage error threshold, the battery under test remains in a continuous testing state. Only the fifth and sixth open-circuit voltages need to be measured at the termination and start temperatures. The self-discharge effect is estimated and corrected using the slope averaging method. This method eliminates the need for time-consuming state resets, significantly shortening the testing cycle and improving testing efficiency. Attached Figure Description

[0024] Figure 1 This is a schematic flowchart of a battery open-circuit voltage temperature compensation measurement method based on bidirectional temperature scanning provided in an embodiment of this application; Figure 2 This is a schematic diagram of the temperature rise of a battery open-circuit voltage temperature compensation measurement method based on bidirectional temperature scanning provided in an embodiment of this application; Figure 3 This is a cooling schematic diagram of a battery open-circuit voltage temperature compensation measurement method based on bidirectional temperature scanning provided in an embodiment of this application; Figure 4 This is a schematic diagram of the structure of an electronic device disclosed in an embodiment of this application.

[0025] Explanation of reference numerals in the attached figures: 400, electronic device; 401, processor; 402, memory; 403, user interface; 404, network interface; 405, communication bus. Detailed Implementation

[0026] To enable those skilled in the art to better understand the technical solutions in this specification, the technical solutions in the embodiments of this specification will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments.

[0027] In the description of the embodiments of this application, the words "for example" or "for instance" are used to indicate examples, illustrations, or explanations. Any embodiment or design that is described as "for example" or "for instance" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or design options. Rather, the use of the words "for example" or "for instance" is intended to present the relevant concepts in a specific manner.

[0028] In the description of the embodiments of this application, the term "multiple" means two or more. For example, multiple systems means two or more systems, and multiple screen terminals means two or more screen terminals. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. The terms "comprising," "including," "having," and variations thereof all mean "including but not limited to," unless otherwise specifically emphasized.

[0029] Therefore, how to address the inability to separate the effects of temperature and self-discharge in existing technologies is a pressing issue. This application provides a method for measuring the open-circuit voltage temperature compensation of a battery based on bidirectional temperature scanning. Figure 1 This is a flowchart illustrating a battery open-circuit voltage temperature compensation measurement method based on bidirectional temperature scanning, provided in an embodiment of this application. (Refer to...) Figure 1 The method includes the following steps S101-S109.

[0030] S101: Place the battery under test in a preset charged state in an initial temperature environment for a preset time, and measure the first open circuit voltage.

[0031] In step S101 above, the battery under test is charged to a preset state of charge (SOC) at room temperature. The preset SOC should avoid the plateau region of the open-circuit voltage-SOC curve for lithium iron phosphate batteries. This is because the open-circuit voltage changes very little when the SOC changes significantly within the plateau region, making it less sensitive to changes in SOC and affecting the accuracy and reliability of subsequent temperature-related measurements. After charging, the battery needs to be allowed to stand at room temperature to eliminate concentration polarization and electrochemical polarization effects generated inside the battery during charging, ensuring a more uniform lithium-ion concentration distribution and quasi-equilibrium electrochemical reactions on the electrode surfaces.

[0032] The battery under test is placed in a temperature-controlled constant-temperature chamber, with the chamber temperature set to the initial temperature, such as 22°C, and then enters a 12-hour settling period. The reason for this relatively long settling time is that, as a system with a certain heat capacity, the battery requires a heat conduction process from the surface to the center to establish its internal temperature field. This is especially true for cells with larger capacity or thicker dimensions, where a sufficiently long time is needed for the internal temperature to reach complete thermal equilibrium with the ambient temperature. Only when the temperature of all parts of the battery is completely uniform and equal to the initial temperature can the measured open-circuit voltage truly reflect the battery's electromotive force characteristics under that temperature condition. During the 12-hour settling period, the constant-temperature chamber maintains a constant initial temperature, and the battery under test gradually transitions from an initial state of uneven temperature distribution to a steady state with a completely uniform temperature field. Simultaneously, any residual polarization effect further dissipates during this process. After the preset 12-hour settling period, the terminal voltage of the battery under test is measured and recorded using a high-precision voltage measuring device. At this time, since the battery is in an open circuit state and the internal and external temperatures are completely consistent and the polarization effect has been fully eliminated, the measured voltage is the actual first open circuit voltage at the initial temperature and the preset charging state.

[0033] This fully static method ensures that the measured value of the first open-circuit voltage is not affected by temperature gradient and polarization interference, laying a reliable data foundation for the accurate separation of temperature influence and self-discharge influence during subsequent bidirectional temperature scanning, and significantly improving the accuracy and repeatability of the entire measurement method.

[0034] S102: Adjust the ambient temperature of the battery under test to the termination temperature, let it stand for a preset time, and measure the second open circuit voltage.

[0035] In step S102 above, after measuring the first open-circuit voltage, the ambient temperature of the battery under test needs to be adjusted to achieve the heating process of the first temperature scan path. By adjusting the temperature setting of the constant temperature chamber, the ambient temperature is gradually increased from the initial temperature, such as 22°C, to the final temperature, such as 28°C. During the ambient temperature adjustment process, the air temperature inside the constant temperature chamber first increases in response to the change in the temperature setting. Heat is transferred to the battery under test through convection and heat conduction, causing the surface temperature of the battery to gradually increase. Then, through the heat conduction process inside the battery, the temperature distribution of the entire battery cell transitions from the original initial temperature state to the new temperature distribution state. Since there is a significant temperature gradient inside the battery in the initial stage of temperature change, with the surface temperature higher than the center temperature, and this temperature non-uniformity leads to differences in the electrochemical equilibrium state at different locations inside the battery, thus affecting the accuracy of the open-circuit voltage measurement, it is necessary to continue to let the battery stand for a preset time, i.e., 12 hours, after the ambient temperature is adjusted to the final temperature to ensure that the internal temperature field of the battery under test reaches a uniform and stable state again.

[0036] During the 12-hour settling period, the constant temperature chamber maintained a constant output at the termination temperature. The temperature gradient inside the battery gradually disappeared, and eventually the temperature of the entire battery cell from the surface to the center became completely uniform and equal to the termination temperature. At this point, the electrochemical system inside the battery re-established thermodynamic equilibrium under the new temperature conditions. Simultaneously, during this settling process, the transient polarization effect that might have been caused by temperature changes gradually dissipated over time, and the charge distribution and ion concentration distribution on the electrode surface tended to a stable equilibrium state. After the preset 12-hour settling period, the terminal voltage of the battery under test was measured using a high-precision voltage measuring device and recorded as the second open-circuit voltage. Since the battery had reached complete thermal and electrochemical equilibrium at the termination temperature, the measured second open-circuit voltage accurately reflects the intrinsic electromotive force characteristics of the battery under test at the termination temperature and the preset state of charge.

[0037] By comparing the first open-circuit voltage with the second open-circuit voltage, the change in open-circuit voltage of the battery under test between the start temperature and the end temperature was initially obtained. This change includes both the voltage change caused by the temperature rising from the start temperature to the end temperature and the voltage drop caused by self-discharge during the total 24-hour rest period. This provides the first set of key data for subsequently removing the effect of self-discharge through differential calculations using bidirectional temperature scanning. Figure 2 As shown, Figure 2 The voltage-temperature characteristics of the battery under test are shown along its heating path. The horizontal axis represents the temperature range from 22°C to 28°C, and the vertical axis represents the open-circuit voltage range from 3.930 volts to 3.960 volts. The starting point, labeled OCV1, is located at 22°C, corresponding to a voltage of approximately 3.957 volts, representing the measured value of the first open-circuit voltage at the starting temperature. The ending point, labeled OCV2, is located at 28°C, corresponding to a voltage of approximately 3.930 volts, representing the measured value of the second open-circuit voltage at the ending temperature. The black straight line between the two points exhibits a distinct negative slope, indicating that the open-circuit voltage decreases linearly with increasing temperature. The blue arrow V1 indicates that the voltage difference extending vertically upwards from point OCV2 to the horizontal line where point OCV1 is located is approximately 27 millivolts, visually demonstrating the voltage reduction caused by temperature changes during the heating process.

[0038] S103: Obtain the open-circuit voltage curve of the battery under test at standard temperature, extract the slope of the curve corresponding to the preset state of charge, and retrieve the hysteresis difference and high-temperature aging value corresponding to the material of the battery under test.

[0039] In the above S103, after completing the first set of data acquisition for bidirectional temperature scanning, in order to accurately predict the voltage error that may occur during the measurement process and select the optimal test strategy, the open circuit voltage curve of the battery under test at the standard temperature is obtained, and the slope of the curve corresponding to the preset state of charge is extracted. At the same time, the hysteresis difference and high temperature aging value corresponding to the material of the battery under test are retrieved.

[0040] The process involves obtaining the open-circuit voltage curve of the battery under test at a standard temperature and extracting the slope of the curve corresponding to a preset state of charge (SOC). Specifically, this includes: acquiring the first voltage and SOC data of the battery under test during discharge at a standard temperature; charging the battery under test with a constant current until the charging cutoff condition, and acquiring the second voltage and SOC data during the charging process; calculating the arithmetic mean of the first voltage and the second voltage under the same SOC, and fitting the arithmetic mean of each SOC point to generate the open-circuit voltage curve at the standard temperature; determining the target voltage point corresponding to the preset SOC on the open-circuit voltage curve; selecting the first SOC point and the second SOC point within a preset neighborhood of the preset SOC, and obtaining the first voltage value corresponding to the first SOC point and the second voltage value corresponding to the second SOC point from the open-circuit voltage curve; and dividing the difference between the first voltage value and the second voltage value by the difference between the first SOC point and the second SOC point to obtain the slope of the curve corresponding to the preset SOC.

[0041] Specifically, after fully charging the battery under test, it is placed in a constant temperature chamber at a standard temperature, such as 2°C, for sufficient settling. Once the internal temperature of the battery is completely uniform and reaches the standard temperature, the battery is discharged using a constant small current. The discharge current is typically selected to be about one-twentieth of the battery's rated capacity to minimize the impact of current polarization. Throughout the discharge process, the battery testing system collects and records the terminal voltage data and the corresponding state of charge (SOC) data of the battery under test in real time. The SOC data can be calculated by integrating the discharge current over time and dividing by the battery's rated capacity. Because a very low discharge rate is used and the battery is always in a standard temperature environment, the measured terminal voltage is relatively close to the true open-circuit voltage characteristics. These data are recorded as the first voltage and SOC data set. When the discharge process continues until the battery reaches the discharge cutoff voltage, the discharge process ends. At this point, the corresponding data of the first voltage and SOC over the entire SOC range from fully charged to depleted is obtained.

[0042] The battery under test was charged with a constant current to obtain voltage characteristic data under the charging path. Before charging, the battery under test was placed at a standard temperature for a certain period of time to eliminate the residual polarization effect from the discharge process. The battery under test was charged with a constant small current of the same order of magnitude as the discharge current. The charging process was also carried out in a constant temperature chamber at a standard temperature to maintain consistent temperature conditions. During the charging process, the battery testing system collected and recorded the terminal voltage data and the corresponding state of charge (SOC) data of the battery under test in real time. The SOC was also calculated by integrating the charging current over time. The charging process ended when the charging cutoff condition was met, such as reaching the charging cutoff voltage or the charging current dropping below a set threshold. At this point, the relationship between the second voltage and the SOC was obtained for the entire SOC range from empty state to fully charged state. Due to the inherent charge and discharge hysteresis effect of materials such as lithium iron phosphate batteries, the second voltage measured during the charging process is usually higher than the first voltage measured during the discharge process under the same SOC. This difference is not a true open-circuit voltage characteristic but a hysteresis phenomenon caused by changes in electrode material structure and differences in ion diffusion paths.

[0043] To eliminate the influence of charge / discharge hysteresis on the open-circuit voltage curve, it is necessary to perform arithmetic averaging on the first voltage and state-of-charge (SOC) data, as well as the second voltage and SOC data. The first and second voltage and SOC data are aligned according to their SOC values. For each specific SOC value, the corresponding first voltage value is found in the first voltage and SOC data, and the corresponding second voltage value is found in the second voltage and SOC data. The arithmetic mean of these two voltage values ​​is then calculated as the hysteresis-corrected open-circuit voltage value for that SOC state. By performing the above averaging on all data points across the entire SOC range, an arithmetic mean data set corresponding to each SOC point is obtained. This data set accurately reflects the intrinsic relationship between the open-circuit voltage and SOC of the battery under test at standard temperatures, effectively eliminating the systematic bias caused by differences in charge / discharge paths. The arithmetic mean of each state of charge is used as discrete data points. Polynomial fitting, spline interpolation or other mathematical fitting methods are used to fit these discrete points to generate a continuous and smooth open-circuit voltage curve at a standard temperature. This curve covers the complete voltage characteristics from zero charge to full charge.

[0044] After obtaining the open-circuit voltage curve at standard temperature, the target voltage point corresponding to the preset state of charge (SOC) is determined on the open-circuit voltage curve. This is achieved by locating the preset SOC position on the horizontal axis of the open-circuit voltage curve (the SOC axis) based on the preset SOC value set in the previous steps. The vertical axis corresponding to this SOC, i.e., the voltage value, is then calculated using the curve equation or interpolation. This voltage value is the target voltage point corresponding to the preset SOC. To extract the slope of the curve at this target voltage point to quantify the sensitivity of the open-circuit voltage to changes in the SOC, two neighboring SOC points within a preset neighborhood of the preset SOC are selected for local slope calculation. This preset neighborhood is typically set to a SOC range of 2% to 5% above and below the preset SOC value. This ensures that the neighborhood is small enough to accurately reflect the local characteristics at the target point, while avoiding an excessively small neighborhood that could amplify the error in numerical differentiation. Within a preset neighborhood, a first state of charge (SOC) point located below the preset SOC and a second SOC point located above the preset SOC are selected. These two SOC points are approximately symmetrically distributed about the preset SOC. The first voltage value corresponding to the first SOC point and the second voltage value corresponding to the second SOC point are obtained from the open-circuit voltage curve using curve equations or interpolation methods. The difference between the first and second voltage values ​​is taken as the voltage change, and the difference between the first and second SOC points is taken as the SOC change. Dividing the two yields the slope of the curve corresponding to the preset SOC. The physical meaning of this slope is the change in open-circuit voltage caused by a unit SOC change near the preset SOC. The absolute value reflects the sensitivity of the open-circuit voltage at that SOC point to capacity changes; a larger absolute value of the slope indicates a larger voltage deviation for the same capacity loss.

[0045] Simultaneously, it is necessary to retrieve the hysteresis difference and high-temperature aging value corresponding to the material of the battery under test from the battery material database or historical test data. The hysteresis difference refers to the typical value of the additional deviation of the open-circuit voltage caused by the difference in the phase transition path of the electrode material and the ion diffusion lag effect after the battery material undergoes a temperature change process. This parameter is usually obtained through statistical testing of a large number of batteries of the same type and stored in a database. The high-temperature aging value is the irreversible capacity decay rate of the material under specific high-temperature conditions, calculated based on the Arrhenius equation. It reflects the rate of permanent capacity loss caused by irreversible aging reactions such as solid electrolyte interfacial film growth and active material decomposition during high-temperature static storage. By obtaining these three key parameters—curve slope, hysteresis difference, and high-temperature aging value—it is possible to predict the amount of voltage error that may occur before conducting a complete bidirectional temperature scan test based on the battery characteristics and test conditions. This allows for the intelligent selection of whether to use the difference method or the slope averaging method, thereby optimizing the test process and time cost while ensuring measurement accuracy.

[0046] S104: Calculate the curve slope, hysteresis difference, and high-temperature aging value to obtain the current expected voltage error.

[0047] In S104 above, the curve slope, hysteresis difference, and high-temperature aging value are calculated to obtain the current expected voltage error. Specifically, this includes: obtaining the reversible self-discharge rate of the battery under test at the test temperature, the estimated time spent at the target temperature, and the hysteresis activation coefficient; adding the reversible self-discharge rate to the high-temperature aging value to obtain the total capacity loss rate, where the high-temperature aging value is the irreversible aging rate calculated based on the Arrhenius equation; multiplying the absolute values ​​of the total capacity loss rate, the estimated time, and the curve slope to obtain the first voltage error term; multiplying the hysteresis activation coefficient and the hysteresis difference to obtain the second voltage error term; and adding the first voltage error term and the second voltage error term to obtain the current expected voltage error.

[0048] Specifically, the reversible self-discharge rate of the battery under test is obtained at the test temperature. This test temperature should be the highest test temperature during the entire temperature scan. For example, in the temperature scan scheme with an initial temperature of 22°C and an ending temperature of 28°C, the test temperature is 28°C. This is because the self-discharge rate increases with temperature, and calculating the self-discharge rate at the highest temperature provides the most conservative error estimate, ensuring that the actual error risk is not underestimated. The reversible self-discharge rate is usually obtained through historical test data. This involves placing a battery of the same type under test in an open circuit at the test temperature for an extended period and periodically measuring its open circuit voltage or state of charge change. The percentage of capacity loss per unit time is taken as the reversible self-discharge rate at that temperature, expressed as percent per hour. For example, the reversible self-discharge rate of a lithium iron phosphate battery at 28°C is measured to be 0.02 percent per hour. Simultaneously, it is necessary to determine the estimated time the battery under test will remain at the target temperature, which is also a high temperature, i.e., 28°C. The estimated time refers to the cumulative time required for the battery under test to reach thermal equilibrium under this high temperature condition during the bidirectional temperature scan. For example, in the above scheme, after heating from 22°C to 28°C, it needs to remain for 12 hours, so the estimated time is 12 hours. The accurate setting of this parameter directly affects the integral accumulation effect of the capacity loss rate on the total capacity loss. In addition, it is necessary to obtain the hysteresis activation coefficient. This coefficient is a dimensionless parameter, usually ranging from 0 to 1, used to characterize the degree of activation of the charge-discharge hysteresis effect of the battery material during the temperature change process. When the battery undergoes the temperature scan process, the temperature change will cause the phase transition path inside the electrode material to change, and the crystal structure will produce stress changes, thereby activating or inhibiting the hysteresis difference originally measured under isothermal conditions to varying degrees. The closer the value of the hysteresis activation coefficient is to 1, the higher the degree of activation of the hysteresis effect by the temperature change; conversely, the closer it is to 0, the smaller the effect of the temperature change on the hysteresis.

[0049] The formula for calculating the current expected voltage error is as follows: ; Where |d(OCV / d(SOC)| represents the absolute value of the slope of the open-circuit voltage curve at the preset state of charge, in mV / %; The estimated time the battery under test will remain at the target temperature is expressed in hours (h); r(Tmax) represents the reversible self-discharge rate of the battery under test at the test temperature, expressed in %h. The Arrhenius equation is used to quantify the irreversible aging rate caused by high temperature, in %h; Tmax represents the absolute height of the test temperature; Ea represents the activation energy of the side reaction; R represents the ideal gas constant; A represents the pre-factor; Vst(SOC) represents the material hysteresis, in mV; a represents the hysteresis activation coefficient.

[0050] After obtaining the above parameters, substitute them into the above calculation formula to start the calculation of the first voltage error term. This error term reflects the open-circuit voltage deviation caused by two capacity loss mechanisms: reversible self-discharge and irreversible aging. First, add the reversible self-discharge rate to the high-temperature aging value to obtain the total capacity loss rate. The high-temperature aging value is the irreversible aging rate calculated based on the Arrhenius equation. The specific calculation formula is that the high-temperature aging value is equal to the pre-exponential factor multiplied by the natural exponential function. The exponential part of the exponential function is the negative activation energy divided by the product of the ideal gas constant and the absolute temperature of the test temperature, i.e., A multiplied by exp(-Ea) divided by R multiplied by Tmax. Here, A is the pre-exponential factor reflecting the intrinsic aging tendency of the material, Ea is the activation energy of the side reaction, which is usually between 0.4 and 0.8 eV, R is the ideal gas constant, which is taken as 8.314 joules per mole per Kelvin, and Tmax is the absolute temperature of the test temperature, i.e., the Celsius temperature plus 273.15, for example, 28℃ corresponds to 301.15 Kelvin. The high-temperature aging value calculated using the Arrhenius equation is also in percent per hour. For example, the high-temperature aging value of a certain lithium iron phosphate battery at 28°C is calculated to be 0.01 percent per hour. Adding this value to the aforementioned reversible self-discharge rate of 0.02 percent per hour, we get the total capacity loss rate as 0.03 percent per hour. This total capacity loss rate comprehensively reflects the superposition effect of the two capacity decay mechanisms, reversible and irreversible. The total capacity loss rate, estimated time, and absolute value of the curve slope are multiplied together. The absolute value of the curve slope represents the voltage change caused by a unit capacity change near the preset state of charge, expressed in millivolts per percentage. For example, if the absolute value of the curve slope is 50 millivolts per percentage at a state of charge point that avoids a plateau, the first voltage error term is calculated by multiplying the total capacity loss rate of 0.03 percent per hour, the estimated time of 12 hours, and the absolute value of the curve slope of 50 millivolts per percentage. This first voltage error term means that during the 12-hour high-temperature static period, reversible self-discharge and irreversible aging together cause the tested battery to lose 0.36 percent of its state of charge. This loss of state of charge corresponds to an 18-mV drop in open-circuit voltage near the preset state of charge. This error is directly added to the actual effect of temperature on the open-circuit voltage, causing measurement deviation.

[0051] Next, the second voltage error term is calculated. This term reflects the impact of the charge-discharge hysteresis effect activated during temperature changes on the open-circuit voltage measurement. The hysteresis activation coefficient and the hysteresis difference are multiplied together. The hysteresis difference is a typical open-circuit voltage hysteresis deviation of this type of battery after temperature changes, retrieved from the material database, and is expressed in millivolts (mV). For example, the hysteresis difference of a certain lithium iron phosphate battery is 10 mV. The hysteresis activation coefficient is determined based on the temperature change amplitude and rate. Assuming that the hysteresis activation coefficient is 0.5 during this 6°C temperature change, the second voltage error term is 0.5 multiplied by 10, which equals 5 mV. The physical meaning of this error term is that during the temperature change from 22°C to 28°C, the temperature gradient and the rate of temperature change disturb the microstructure of the electrode material, causing the 10 mV hysteresis difference originally reflected in the isothermal charge-discharge cycle to be activated by 50%, or 5 mV. This voltage deviation caused by hysteresis activation will also interfere with the accurate measurement of the pure influence of temperature. Adding the first voltage error term to the second voltage error term yields the current expected voltage error, which in the example above is 18 mV plus 5 mV equals 23 mV. This current expected voltage error comprehensively quantifies the overall impact of the three mechanisms of reversible self-discharge, irreversible aging, and hysteresis activation on the open-circuit voltage measurement under the current test conditions, providing a quantitative criterion for subsequent judgment on whether the complete bidirectional temperature scan difference method needs to be used.

[0052] Furthermore, the hysteresis activation coefficient of the battery under test is obtained, specifically including: obtaining the absolute temperature difference between the initial temperature and the target temperature; dividing the absolute temperature difference by the reference temperature span to obtain the temperature activation factor; obtaining the estimated time for the battery under test to stand at the target temperature, and dividing the estimated time by the hysteresis relaxation time constant to obtain the time ratio; calculating the power function value of the natural constant with the negative of the time ratio as the exponent, and subtracting the power function value from 1 to obtain the time relaxation factor; multiplying the temperature activation factor and the time relaxation factor to obtain the hysteresis activation coefficient.

[0053] Specifically, in calculating the current expected voltage error, the hysteresis activation coefficient is a key parameter for quantifying the activation degree of the battery's charge-discharge hysteresis effect due to temperature changes. The hysteresis activation coefficient needs to be accurately calculated by comprehensively considering the effects of both the magnitude of temperature change and the resting time. The calculation of the hysteresis activation coefficient is necessary because the charge-discharge hysteresis effect of battery materials is not constant but dynamically adjusts with temperature changes and time evolution. When the battery undergoes a temperature scan, temperature changes disturb the phase transition path and ion diffusion kinetics of the electrode materials. The activation degree of this disturbance effect depends on both the magnitude of the temperature change and the length of the resting relaxation time at the new temperature. Only by quantitatively modeling the coupling effect of these two factors can the actual impact of the hysteresis effect on open-circuit voltage measurement be accurately predicted.

[0054] The absolute temperature difference between the initial temperature and the target temperature is obtained. This absolute temperature difference directly reflects the temperature change range during the temperature scanning process and is the driving force for activating the hysteresis effect. In the above embodiment, the initial temperature is 22°C, and the target temperature is a high temperature of 28°C. The absolute temperature difference between the two is obtained by subtracting the absolute value of the initial temperature from the target temperature. That is, the absolute value function calculation of 28 minus 22 equals 6°C. This 6°C temperature span characterizes the degree of thermodynamic state change experienced by the battery during the heating process. The larger the temperature span, the stronger the thermal disturbance to the microstructure of the electrode material, and thus the more significant the activation effect of the hysteresis effect. The temperature activation factor is obtained by dividing the absolute temperature difference by the reference temperature span. The reference temperature span is a pre-set temperature scaling parameter used to normalize the actual temperature change range to a dimensionless range of zero to one for subsequent calculations. The reference temperature span is usually set according to the characteristics of the battery material and the application scenario. For example, for lithium iron phosphate batteries, the reference temperature span can be set to 10°C. This value represents that the hysteresis activation effect reaches a near-saturation state within a temperature change range of 10°C. Dividing the aforementioned absolute temperature difference of 6°C by the reference temperature span of 10°C yields a temperature activation factor of 0.6. The physical meaning of this temperature activation factor is that the current temperature change range has reached 60% of the activation intensity relative to the reference temperature span, indicating that the temperature change has a moderate activation effect on the hysteresis effect but has not yet reached a fully saturated state.

[0055] After obtaining the temperature activation factor, it is also necessary to consider the modulation effect of the time dimension on the hysteresis activation. Even if the same temperature change has occurred, if the resting time at the new temperature is insufficient, the phase transition process and ion redistribution process inside the electrode material have not yet completed relaxation, and the activation degree of the hysteresis effect will be suppressed. Therefore, it is necessary to introduce a time relaxation factor to correct the temperature activation factor. The estimated resting time of the battery under test at the target temperature is obtained. This estimated time is the resting time required to reach thermal equilibrium at a high temperature of 28°C, for example, 12 hours. Then, this estimated time is divided by the hysteresis relaxation time constant to obtain the time ratio. The hysteresis relaxation time constant is a material parameter that characterizes the characteristic time required for the internal phase transition and ion diffusion of the battery material to reach a new equilibrium state after a temperature change. This parameter is usually determined by a temperature jump experiment, that is, after the battery changes abruptly from one temperature to another, the evolution curve of the open circuit voltage over time is continuously monitored, and the time corresponding to the voltage change decaying to 63% of the final steady-state value is taken as the hysteresis relaxation time constant. For a typical lithium iron phosphate battery, this time constant is about 6 to 8 hours. Assuming that the hysteresis relaxation time constant is 8 hours in this example, the time ratio is the estimated time of 12 hours divided by the hysteresis relaxation time constant of 8 hours, which equals 1.5. This time ratio indicates that the actual resting time is 1.5 times the characteristic time required to reach relaxation equilibrium. Next, we calculate the power function value of the natural constant with the negative of the time ratio as the exponent, i.e., exp -1.5, where exp represents the natural exponential function and e is approximately equal to 2.718. The result is exp -1.5, which is approximately equal to 0.223. This power function value reflects the proportion of the hysteresis effect that has not yet completed relaxation at the current resting time. Then, we subtract this power function value from 1 to obtain the time relaxation factor, i.e., 1 minus 0.223 equals 0.777. The physical meaning of this time relaxation factor is that after 12 hours of resting, the hysteresis activation process has completed approximately 77.7% of the relaxation evolution, approaching but not yet reaching the final equilibrium state. The closer its value is to 1, the more complete the relaxation, and the closer the activation degree of the hysteresis effect is to the limit determined by the temperature change amplitude.

[0056] Multiplying the temperature activation factor by the time relaxation factor yields the hysteresis activation coefficient, which in the example above is approximately 0.466 (0.6 multiplied by 0.777). This hysteresis activation coefficient comprehensively quantifies the coupled effect of temperature change amplitude and resting relaxation time on the activation of the hysteresis effect. The value is between 0 and 1. When the hysteresis activation coefficient is close to 0, it indicates that the temperature change amplitude is very small or the resting time is extremely short, resulting in almost no hysteresis activation. At this time, the interference of the hysteresis difference on the open-circuit voltage measurement can be ignored. However, when the hysteresis activation coefficient is close to 1, it indicates that the temperature change amplitude is large and after sufficient resting relaxation, the hysteresis effect is fully activated. At this time, the full influence of the material's inherent hysteresis difference needs to be considered.

[0057] S105: Compare the current expected voltage error with the maximum voltage error threshold.

[0058] In step S105 above, the maximum voltage error threshold is first determined. This threshold is a pre-set voltage criterion parameter used to define the upper limit of tolerable measurement error. The value setting needs to comprehensively consider the accuracy requirements of the temperature compensation coefficient measurement and the actual application needs of the battery management system. Combining the absolute value of the curve slope in the above embodiment, which is 50 mV per percentage point, if the deviation in state of charge caused by the temperature compensation coefficient measurement error is required to be no more than 0.2 percent, then the corresponding voltage error tolerance is 0.2 percent multiplied by 50 mV per percentage point, which equals 10 mV. Therefore, the maximum voltage error threshold can be set to 10 mV. This threshold value indicates that when the combined voltage error caused by various interference mechanisms does not exceed 10 mV, the slope averaging method can still meet the measurement accuracy requirements. However, when the voltage error exceeds 10 mV, the difference method must be used to suppress the interference effect. In different application scenarios, the maximum voltage error threshold can be adjusted according to the actual accuracy requirements. For example, in scenarios where the accuracy requirements are not high, the threshold can be relaxed to 15 millivolts or even 20 millivolts, while in scenarios where the accuracy requirements are extremely high, the threshold may need to be tightened to 5 millivolts.

[0059] After determining the maximum voltage error threshold, the calculated current expected voltage error is compared with the maximum voltage error threshold. Taking the above embodiment as an example, the calculated current expected voltage error is 23 millivolts, and the maximum voltage error threshold is set to 10 millivolts. By comparison, it is determined that the current expected voltage error of 23 millivolts is greater than the maximum voltage error threshold of 10 millivolts.

[0060] S106: If the current expected voltage error is greater than the maximum voltage error threshold, the state of the battery under test is reset, the reset battery under test is placed at the termination temperature and left to stand for a preset time, the third open circuit voltage is measured, the ambient temperature of the battery under test is adjusted to the starting temperature and left to stand for a preset time, and the fourth open circuit voltage is measured.

[0061] In S106 above, when the current expected voltage error is determined to be greater than the maximum voltage error threshold, the complete bidirectional temperature scan difference method test process will be automatically triggered. This effectively eliminates the influence of interference factors such as self-discharge, aging, and hysteresis through symmetrical path design and difference calculation, ensuring that the high-precision requirements of temperature compensation coefficient measurement are met. In the above embodiment, the calculated current expected voltage error is 23 mV, which exceeds the maximum voltage error threshold of 10 mV. This indicates that the interference effect accumulated during the first temperature scan is too large. If the calculation is based solely on the data from the first heating path, the measurement results will be severely distorted. Therefore, a second cooling path scan in the opposite direction to the first scan must be performed. The interference factors are eliminated through the difference calculation of the two scan data. This requires that the state of the battery under test be reset before starting the second scan, so that the battery is restored to the same initial state as when the first scan began, thereby ensuring that the test conditions of the two scans are strictly comparable and symmetrical.

[0062] The necessity of a state reset operation lies in the fact that after the first temperature-up scan, the state of charge of the battery under test has deviated from the initial preset state of charge due to self-discharge and irreversible aging. Simultaneously, the battery is currently in a thermodynamic state at the termination temperature (high temperature 28°C), and the internal electrode material phase distribution, ion concentration distribution, and interface layer structure all differ from the initial state. If the second temperature-down scan is performed directly from the current state, the starting states of the two scans will be different, making it impossible to guarantee the symmetry of the temperature's influence on open-circuit voltage and the consistency of the self-discharge's influence. Consequently, the difference calculation cannot effectively eliminate interference factors. Therefore, a state reset is needed to restore the battery to its initial state. The battery to be tested is removed from the constant temperature chamber and transferred to a room temperature environment. Then, the discharge equipment is started to discharge the battery, completely releasing the remaining charge to a near-zero state of charge. This discharge process usually adopts a constant current discharge method, with the discharge current set at a moderate rate between 0.2C and 0.5C. This ensures that the discharge is completed within a reasonable time without causing severe concentration polarization and ohmic polarization effects inside the battery due to excessive discharge rate. The discharge process continues until the battery terminal voltage drops to the discharge cutoff voltage. For lithium iron phosphate batteries, this cutoff voltage is usually set between 2.5V and 2.8V. Once the cutoff voltage is reached, the discharge is stopped immediately, and the battery is left to stand at room temperature for 1 to 2 hours to fully eliminate the polarization effect accumulated during the discharge process. At this time, the battery's state of charge is close to zero, and almost all the lithium ions inside are embedded in the negative electrode material, while the positive electrode material is in a delithiation state. The electrochemical state of the battery has returned to a clear baseline.

[0063] After the discharge operation is completed, the battery under test is immediately recharged to restore it to the preset state of charge (SOC). The preset SOC must be exactly the same as the preset SOC adjusted before the first temperature scan to ensure that the two scans are performed at the same SOC point, thereby ensuring the consistency of the open-circuit voltage-SOC curve slope. During the charging operation, a constant charging current is applied to the battery through the charging equipment. The charging current is also set to a moderate rate of 0.2C to 0.5C. The cumulative charging capacity of the battery is monitored in real time during the charging process. When the cumulative capacity reaches the product of the battery's rated capacity and the preset SOC percentage, for example, for a battery with a rated capacity of 50 amp-hours and a preset SOC of 40%, charging is stopped when the cumulative charging capacity reaches 50 amp-hours multiplied by 40% equals 20 amp-hours. At this point, the battery's SOC is precisely controlled at 40%. During charging, it is also necessary to ensure that the charging environment temperature is maintained at around 22°C to avoid the impact of temperature fluctuations on the internal electrochemical reaction kinetics of the battery. After charging, the battery should also be left to stand at room temperature for 1 to 2 hours to allow the concentration polarization and charge transfer polarization generated during charging to be fully eliminated. Once the battery reaches a stable quasi-equilibrium state, the state reset operation is complete. Through the complete cycle of discharging and recharging described above, the battery's state of charge, temperature state, and polarization state are restored to the exact same initial conditions as before the first scan, providing a strictly consistent starting point for the subsequent second temperature scan.

[0064] After resetting the state, in order to achieve a temperature scan direction opposite to the first scan, the reset battery under test needs to be placed directly in the termination temperature environment, instead of being left to stand at the starting temperature as in the first scan. This difference in starting temperature is the key to constructing a symmetrical scan path. The battery, after being reset and left to stand at room temperature, is immediately transferred to the temperature chamber. The temperature control setting of the temperature chamber is adjusted to the termination temperature, i.e., 28°C. Since the battery has just been transferred from the room temperature environment, its initial temperature is about 22°C. After entering the 28°C temperature chamber, the battery temperature will gradually rise. This temperature rise process is physically the same as the temperature rise process from the starting temperature to the termination temperature in the first scan, except that it occurs at the beginning stage of the second scan rather than the measurement stage. The battery is placed in a temperature chamber at a termination temperature of 28°C for a preset time. This preset time is consistent with the placement time at each temperature point during the first scan, for example, 12 hours. The setting of this placement time needs to ensure that the internal temperature of the battery is completely uniform and reaches a thermal equilibrium state consistent with the ambient temperature. For a 50 Ah-level square battery, a placement time of 12 hours is usually sufficient to reduce the temperature difference between the battery core and the surface to within 0.5°C, thus meeting the thermal equilibrium judgment condition.

[0065] Once the preset resting time at the termination temperature has elapsed, immediately activate the voltage measuring device to measure the battery's open-circuit voltage. This open-circuit voltage is recorded as the third open-circuit voltage. A high-precision digital voltmeter with an accuracy better than 1 millivolt is used for the measurement. During measurement, the battery must be disconnected from any charging or discharging equipment to ensure no external current flows through the battery. The measurement should be completed as quickly as possible to avoid changes in temperature and self-discharge state during the measurement process; typically, the measurement time should be controlled within 10 seconds. The third open-circuit voltage reflects the open-circuit voltage value of the battery after a state reset, when it is at 40% of its preset state of charge and has reached thermal equilibrium at the termination temperature of 28°C after 12 hours of resting. This voltage value is affected by the thermodynamic effects caused by temperature increases, changing relative to the voltage at room temperature. Furthermore, self-discharge and irreversible aging-induced voltage decay accumulate during the 12-hour resting period. Therefore, the third open-circuit voltage actually incorporates the combined effects of temperature, self-discharge, and aging.

[0066] After measuring the third open-circuit voltage, the ambient temperature of the battery under test needs to be adjusted to the initial temperature to complete the cooling path for the second scan. The control temperature of the constant temperature chamber is reset to the initial temperature of 22℃. At this time, the temperature inside the chamber will gradually decrease from 28℃. As a material with a certain heat capacity, the temperature change of the battery will lag behind the change of the ambient temperature, requiring a certain amount of heat exchange to reach a new thermal equilibrium. The battery continues to be left to stand at the initial temperature of 22℃ for a preset time, which is also set to 12 hours, consistent with all previous standing stages. This consistency of time parameters is crucial to ensuring the comparability between measurement points. During this 12-hour cooling and standing process, the battery temperature gradually decreases from 28℃ to 22℃. The temperature decrease causes changes in the thermodynamic free energy of the electrode material, which in turn causes a corresponding change in the open-circuit voltage. At the same time, the self-discharge reaction continues during the standing period, further reducing the battery's state of charge and open-circuit voltage. In addition, irreversible side reactions and aging also slowly accumulate. After the battery has been left to stand at the initial temperature for a preset time of 12 hours, the high-precision voltage measuring device is restarted to measure the open-circuit voltage of the battery. The measurement method and accuracy requirements are exactly the same as when measuring the third open-circuit voltage. The open-circuit voltage obtained in this measurement is recorded as the fourth open-circuit voltage. The fourth open-circuit voltage reflects the open-circuit voltage value of the battery under the preset state of charge after the temperature drops from the termination temperature to the initial temperature and after sufficient thermal equilibrium. Due to the effect of temperature reduction, the fourth open-circuit voltage will change relative to the third open-circuit voltage. This change includes both the pure temperature effect caused by the temperature drop of 6°C and the self-discharge and aging effects accumulated during the second 12-hour resting period.

[0067] Through the complete state reset and second temperature scan process described above, two key measurement data points, the third and fourth open-circuit voltages, were obtained. These two data points, together with the first and second open-circuit voltages obtained in the first temperature scan, constitute a complete bidirectional temperature scan dataset. The temperature path of the second scan was from the termination temperature of 28°C to the starting temperature of 22°C, which is completely opposite to the path of the first scan, which was from the starting temperature of 22°C to the termination temperature of 28°C. This reverse path design ensures that the influence of temperature on the open-circuit voltage exhibits an opposite sign but equal absolute value in both scans. That is, if the first temperature increase causes a positive change of T millivolts in the open-circuit voltage, the second temperature decrease will cause a negative change of T millivolts. Meanwhile, time-related interference factors such as self-discharge and aging always have the same direction of action in both scans, leading to a decrease in voltage. Furthermore, since the total resting time for both scans is the same, 24 hours, the battery is in the same state of charge and a similar temperature range. Therefore, the cumulative amounts of self-discharge and aging in the two scans are essentially equal.

[0068] like Figure 3 As shown, Figure 3 This displays the voltage-temperature characteristics of the battery under test as it cools down. The horizontal axis represents the temperature range from 28°C to 22°C. Figure 2 In the opposite direction, the vertical axis represents the open-circuit voltage range from 3.930 volts to 3.960 volts, consistent with the previous graph. The starting point, labeled OCV3, is located at 28°C, corresponding to a voltage of approximately 3.933 volts, representing the measured value of the third open-circuit voltage at the termination temperature. The ending point, labeled OCV4, is located at 22°C, corresponding to a voltage of approximately 3.953 volts, representing the measured value of the fourth open-circuit voltage after returning to the starting temperature. The black straight line between the two points exhibits a positive slope, indicating that the open-circuit voltage increases linearly as the temperature decreases. The blue arrow V2 indicates that the voltage difference extending vertically downwards from point OCV3 to the horizontal line where point OCV4 is located is approximately 20 millivolts, visually demonstrating the amount of voltage increase caused by temperature changes during the cooling process.

[0069] S107: Calculate the self-discharge effect and temperature effect of the battery under test by using the difference method for the first open-circuit voltage, the second open-circuit voltage, the third open-circuit voltage and the fourth open-circuit voltage.

[0070] In S107 above, after completing the bidirectional temperature scan and obtaining four key measurement data points—the first, second, third, and fourth open-circuit voltages—these data are mathematically processed using a difference method. Utilizing the special mathematical relationship constructed by the bidirectional symmetrical scanning path, the pure influence of temperature on the open-circuit voltage is precisely separated from the influence of interfering factors such as self-discharge and aging, thus achieving the core objective of high-precision temperature compensation coefficient measurement. The first heating scan and the second cooling scan are completely opposite in the direction of temperature change, causing the temperature effect to exhibit opposite directions in the two scans. Meanwhile, time-related interfering factors such as self-discharge and irreversible aging maintain the same direction and have essentially equal magnitudes in both scans. This symmetry and consistency provides the mathematical possibility of separating effects through addition and subtraction operations, effectively decoupling multiple physicochemical processes that would otherwise be indistinguishable in a single measurement. The self-discharge effect and temperature effect of the battery under test are calculated by the difference method for the first, second, third, and fourth open-circuit voltages. Specifically, the calculation includes: subtracting the second open-circuit voltage from the first open-circuit voltage to obtain the temperature rise voltage difference; subtracting the third open-circuit voltage from the fourth open-circuit voltage to obtain the temperature fall voltage difference; adding the temperature rise voltage difference and the temperature fall voltage difference and dividing by two to obtain the temperature effect of the battery under test; and subtracting the temperature fall voltage difference from the temperature rise voltage difference and dividing by two to obtain the self-discharge effect of the battery under test.

[0071] Specifically, the first open-circuit voltage is subtracted from the second open-circuit voltage to obtain the temperature rise voltage difference. The physical meaning of this subtraction operation is to calculate the total change in open-circuit voltage experienced by the battery during the first temperature scan, from the initial temperature to the final temperature. Assuming the measured value of the first open-circuit voltage is 3.850 volts, which is the voltage value after the battery reaches thermal equilibrium at the initial temperature, and the measured value of the second open-circuit voltage is 3.844 volts, which is the voltage value after the temperature rises to the final temperature and then reaches thermal equilibrium again, subtracting 3.844 volts from 3.850 volts yields a temperature rise voltage difference of 0.006 volts, or 6 millivolts. The 6 millivolt voltage change is not simply caused by the increase in temperature, but is the result of the combined effects of temperature and self-discharge. Specifically, the increase in temperature from the initial temperature to the final temperature causes a change in the thermodynamic free energy of the electrode material, which in turn causes a change in the open-circuit voltage. At the same time, during the resting period from the measurement of the first open-circuit voltage to the measurement of the second open-circuit voltage, self-discharge and irreversible side reactions continue to occur inside the battery, which leads to a decrease in the effective state of charge and thus a decrease in the open-circuit voltage. Therefore, the voltage difference due to temperature rise actually includes the combined contribution of temperature and self-discharge effects.

[0072] Subtracting the third open-circuit voltage from the fourth open-circuit voltage yields the cooling voltage difference. This subtraction corresponds to the total open-circuit voltage change experienced by the battery during the second temperature scan as it descends from the termination temperature to the starting temperature. Assuming the third open-circuit voltage measurement is 3.848 volts (the voltage after the battery reaches thermal equilibrium at the termination temperature following a state reset), and the fourth open-circuit voltage measurement is 3.852 volts (the voltage after the temperature drops to the starting temperature and is allowed to rest again to reach thermal equilibrium), subtracting 3.848 volts from 3.852 volts gives a cooling voltage difference of 0.004 volts, or 4 millivolts. This 4 millivolt voltage change also includes the superposition of temperature and self-discharge effects. However, the key difference from the heating voltage difference is that the temperature change is in the opposite direction. The temperature drop from the termination temperature to the starting temperature causes the open-circuit voltage to change in the opposite direction to the heating process. During the resting period in the second scan, the self-discharge reaction continues, and its influence on the voltage is consistent with the self-discharge effect in the first scan. This characteristic of opposite temperature effects and the same direction of self-discharge effects highlights this difference.

[0073] The temperature effect of the battery under test is obtained by adding the difference in heating voltage and the difference in cooling voltage and then dividing by two. The mathematical principle of this calculation step is to utilize the characteristic that the temperature effect is opposite in direction in the two scans, and to strengthen the mathematical signal of the temperature effect through addition. In specific calculation, the heating voltage difference of 6 mV and the cooling voltage difference of 4 mV are added to get 10 mV, and then divided by two to get 5 mV. This 5 mV is the temperature effect of the battery under test. From a mathematical derivation perspective, the heating voltage difference can be expressed as the algebraic sum of the temperature effect T and the self-discharge effect D, denoted as T plus D. The cooling voltage difference can be expressed as the algebraic sum of the negative temperature effect negative T and the self-discharge effect D, denoted as negative T plus D. Adding the two together gives T plus D plus negative T plus D, which simplifies to 2D. This shows that the addition operation eliminates the temperature effect with opposite direction and retains the self-discharge effect with the same direction. However, considering the actual definition of the sign and direction of voltage change, this derivation needs to be corrected in conjunction with the specific physical process. The voltage difference of 6 mV during temperature rise reflects the combined result of voltage change caused by temperature rise and voltage drop caused by self-discharge. The voltage difference of 4 mV during temperature drop reflects the combined result of voltage change caused by temperature drop and voltage drop caused by self-discharge. The sum of the two and the result of dividing by two is 5 mV, which actually represents the average voltage change caused purely by temperature factors during the temperature change process, successfully eliminating the interference effect of self-discharge.

[0074] The self-discharge effect of the battery under test is obtained by subtracting the cooling voltage difference from the heating voltage difference and then dividing by two. The mathematical principle of this calculation step is based on the characteristic that the self-discharge effect is in the same direction in the two scans. The temperature effect is eliminated and the self-discharge signal is extracted by subtraction. Subtracting the cooling voltage difference of 4 mV from the heating voltage difference of 6 mV gives 2 mV, which is then divided by two to get 1 mV. This 1 mV is the self-discharge effect of the battery under test. From a mathematical derivation perspective, the heating voltage difference is represented as T plus D, and the cooling voltage difference is represented as negative T plus D. Subtracting the latter from the former gives T plus D minus negative T minus D, which simplifies to 2T. This shows that the subtraction operation eliminates the self-discharge effect in the same direction and retains twice the temperature effect. This result forms a complete mathematical complement to the derivation of the temperature effect mentioned above. In practical physics, the self-discharge effect of 1 millivolt represents the average change in open-circuit voltage caused by self-discharge and irreversible aging reactions during the resting period of each of the two scans. Although this value is relatively small, it is still of great significance for high-precision measurement applications. By using the difference method, this effect was successfully separated from the total voltage change, thus avoiding interference with the measurement of the temperature compensation coefficient.

[0075] Through the complete difference method calculation process described above, two independent physical parameters, namely the temperature effect of 5 mV and the self-discharge effect of 1 mV, can be successfully extracted from the four open-circuit voltage measurements.

[0076] S108: If the current expected voltage error is less than or equal to the maximum voltage error threshold, the battery under test is kept in continuous testing state, and the battery is left to stand for a preset time at the termination temperature to measure the fifth open circuit voltage. The ambient temperature of the battery under test is adjusted to the starting temperature and left to stand for a preset time to measure the sixth open circuit voltage.

[0077] In S108 above, if the current expected voltage error is less than or equal to the maximum voltage error threshold, the battery under test is deemed to have good state stability and an acceptablely low self-discharge rate. The accumulated error in subsequent measurements will not significantly affect the accuracy of the temperature compensation coefficient measurement, and a simplified measurement procedure maintaining continuous testing can be adopted. Specifically, maintaining continuous testing means that from the moment the second open-circuit voltage measurement is completed until all subsequent measurements are completed, the battery under test is neither discharged nor recharged. The battery's state of charge remains near the initially adjusted preset state of charge, allowing only a slow and slight decrease in state of charge due to natural self-discharge. The battery remains in an open-circuit resting state, not connected to any external power source or load. This continuous testing state avoids disturbances to the battery's internal state caused by charge-discharge cycles, eliminates additional uncertainties introduced by factors such as charging termination judgment errors and differences in charging current selection during state reset, and makes the battery state more consistent and comparable throughout the measurement process, laying the foundation for obtaining high-quality temperature compensation coefficient measurement results.

[0078] After confirming continuous testing, the battery was immediately left to stand at the termination temperature for a preset time to measure the fifth open-circuit voltage. The battery under test was currently in an environment with a termination temperature of 28°C after the second open-circuit voltage measurement. No temperature adjustment was needed at this point. The battery was kept in a constant temperature chamber at the termination temperature of 28°C or in an environment maintained at 28°C by a temperature control system, and left to stand at this temperature for the preset time. Since the preset time was set to 12 hours, the battery needed to stand for an additional 12 hours at the termination temperature of 28°C. During these 12 hours, the internal temperature of the battery remained completely balanced with the ambient temperature of 28°C. The thermodynamic and electrochemical equilibrium states of the electrode materials remained stable at the state corresponding to the termination temperature, and there were no transient effects caused by temperature gradients or temperature changes. During this period, the battery continued to undergo self-discharge reactions, and irreversible side reactions of the active materials on the electrode surface and impurity consumption reactions in the electrolyte continued, causing the effective state of charge of the battery to decrease slowly, and the open-circuit voltage to decrease accordingly. Based on the previously estimated self-discharge rate of approximately 0.5 mV per 12 hours, the open-circuit voltage is expected to decrease by approximately 0.5 mV during this additional 12-hour rest period. After the preset 12-hour rest period, the open-circuit voltage of the battery under test is measured using a high-precision voltage measuring device. The internal resistance of the voltmeter in the measuring device must be greater than 1 megohm to ensure that the impact of the measurement process on the battery state is negligible. The measurement time is controlled within 10 seconds to avoid voltage drop caused by the measurement current. The measurement operation is exactly the same as the measurement method for the first and second open-circuit voltages mentioned above to ensure consistency of measurement conditions and comparability of data. The measured voltage value is recorded as the fifth open-circuit voltage, assumed to be 3.847 volts. This 3.847 volts is 1 mV lower than the second open-circuit voltage of 3.848 volts. Unlike the 4 mV voltage change between the two measurements in the first temperature scan, there is no temperature change during the measurement of the fifth open-circuit voltage. Therefore, this 1 mV voltage drop is entirely attributed to the self-discharge effect during the 12-hour rest period.

[0079] The ambient temperature of the battery under test is adjusted to the initial temperature and left to stand for a preset time to measure the sixth open-circuit voltage. After completing the fifth open-circuit voltage measurement, the battery under test is currently in an environment with a termination temperature of 28°C. The ambient temperature needs to be lowered from the termination temperature of 28°C to the initial temperature of 22°C. This temperature environment switch is achieved by removing the battery from the temperature control chamber at the termination temperature and placing it in the temperature control chamber at the initial temperature, or by using a programmable temperature control system to gradually lower the ambient temperature from 28°C to 22°C. The cooling rate is usually controlled at 0.5 to 1°C per minute to avoid stress damage to the battery caused by excessively rapid temperature changes. The temperature needs to be reduced by 6°C from 28°C to 22°C. The cooling process usually takes about 10 to 15 minutes to complete the adjustment of the ambient temperature. Then, it takes about 30 to 60 minutes for the internal temperature of the battery to gradually reach a uniform distribution and complete equilibrium with the ambient temperature. After the ambient temperature stabilized at the initial temperature of 22°C and the battery temperature also reached 22°C, the battery under test was left to stand at this temperature for a preset time of 12 hours. During these 12 hours, the thermodynamic and electrochemical equilibrium states of the battery gradually adjusted to the stable state corresponding to the initial temperature. The temperature drop from 28°C to 22°C caused a change in the free energy of the electrode materials. According to the Nernst equation, a decrease in temperature usually leads to an increase in the open-circuit voltage of a lithium-ion battery. For a temperature decrease of 6°C, if the temperature compensation coefficient is approximately -0.5 mV per°C, the pure temperature effect will lead to an increase in the open-circuit voltage of approximately 3 mV. At the same time, during these 12 hours of resting, the self-discharge reaction continued, which is expected to lead to a decrease in the open-circuit voltage of approximately 0.5 mV. Therefore, under the combined effects of cooling and resting, the change in the sixth open-circuit voltage relative to the fifth open-circuit voltage is the increase of 3 mV caused by the temperature effect minus the decrease of 0.5 mV caused by the self-discharge effect, with an expected net increase of approximately 2.5 mV. After a preset 12-hour settling period, the open-circuit voltage of the battery under test was measured. The measurement conditions and methods were exactly the same as those for the fifth open-circuit voltage measurement. The measured voltage value was recorded as the sixth open-circuit voltage, assumed to be 3.849 volts. This 3.849 volts is 2 millivolts higher than the fifth open-circuit voltage of 3.847 volts. This voltage increase is the result of the combined effects of temperature reduction and self-discharge reduction.

[0080] S109: The slope averaging method is used to calculate the self-discharge effect and temperature effect of the battery under test by calculating the first open-circuit voltage, the second open-circuit voltage, the fifth open-circuit voltage and the sixth open-circuit voltage.

[0081] In S109 above, the slope averaging method is used to calculate the self-discharge effect and temperature effect of the battery under test for the first open-circuit voltage, the second open-circuit voltage, the fifth open-circuit voltage, and the sixth open-circuit voltage. Specifically, this includes: dividing the difference between the fifth open-circuit voltage and the second open-circuit voltage by a first time interval to obtain an estimated value of the self-discharge coefficient in the high-temperature region, where the first time interval is the time interval between the fifth open-circuit voltage and the second open-circuit voltage; and dividing the difference between the sixth open-circuit voltage and the first open-circuit voltage by a second time interval to obtain an estimated value of the self-discharge coefficient in the low-temperature region, where the second time interval is the time interval between the sixth open-circuit voltage and the first open-circuit voltage. Interval; average the estimated self-discharge coefficient in the high-temperature region with the estimated self-discharge coefficient in the low-temperature region to obtain the self-discharge influence; based on the self-discharge influence and the time parameters corresponding to each measurement, calculate the target voltage deviation caused by self-discharge at each measurement point, and subtract the corresponding target voltage deviation from the first open-circuit voltage, second open-circuit voltage, fifth open-circuit voltage, and sixth open-circuit voltage for time correction to obtain multiple corrected open-circuit voltages; based on the temperature difference between the starting temperature and the ending temperature, and the voltage difference between the corresponding corrected open-circuit voltages at different temperatures, calculate the temperature influence of the battery under test.

[0082] Specifically, the difference between the fifth open-circuit voltage and the second open-circuit voltage is divided by the first time interval to obtain an estimated value of the self-discharge coefficient in the high-temperature region. The physical significance of this calculation step is to quantify the self-discharge rate of the battery under test under the termination temperature condition. Both the second and fifth open-circuit voltages are measured at the termination temperature of 28°C, and the voltage difference between them is mainly caused by the self-discharge effect. In the specific calculation, the measured value of the second open-circuit voltage is 3.848 volts, which is the voltage value measured after the battery under test has been left to stand at the termination temperature of 28°C for 12 hours at the end of the first temperature scan. The measured value of the fifth open-circuit voltage is 3.847 volts, which is the voltage value measured after being left to stand at the termination temperature of 28°C for another 12 hours. Subtracting the second open-circuit voltage of 3.848 volts from the fifth open-circuit voltage of 3.847 volts yields -0.001 volts, or -1 millivolt. The first time interval refers to the total time elapsed from the moment the second open-circuit voltage was measured to the moment the fifth open-circuit voltage was measured. This time interval is equal to the preset resting time of 12 hours at the termination temperature. Therefore, the first time interval is 12 hours. Dividing the voltage difference of -1 millivolt by the first time interval of 12 hours yields the estimated self-discharge coefficient for the high-temperature region. The negative value of -1 millivolt divided by 12 hours equals -0.0833 millivolts per hour. This negative sign indicates that the voltage decreases over time. The absolute value of 0.0833 millivolts per hour means that at the termination temperature of 28°C, the self-discharge of the battery under test causes the open-circuit voltage to decrease at a rate of approximately 0.0833 millivolts per hour.

[0083] Dividing the difference between the sixth open-circuit voltage and the first open-circuit voltage by the second time interval yields the estimated value of the self-discharge coefficient in the low-temperature region. The physical meaning of this calculation step is to quantify the comprehensive voltage change rate of the battery under test under the initial temperature conditions. Although named the estimated value of the self-discharge coefficient in the low-temperature region, this value actually includes the combined effects of temperature change and self-discharge. Specifically, the measured value of the first open-circuit voltage is 3.852 volts, which is the voltage value measured after the battery under test has been left to stand at the initial temperature of 22°C for 12 hours at the beginning of the measurement process. The measured value of the sixth open-circuit voltage is 3.849 volts, which is the voltage value measured after heating to the termination temperature, standing twice at the termination temperature, and then cooling back to the initial temperature and standing for 12 hours. Subtracting the first open-circuit voltage of 3.852 volts from the sixth open-circuit voltage of 3.849 volts yields -0.003 volts, or -3 millivolts. The second time interval refers to the total time elapsed from the moment the first open-circuit voltage is measured to the moment the sixth open-circuit voltage is measured. This time interval includes a preset time of 12 hours for the first temperature rise and resting, a preset time of 12 hours for continuing to rest at the termination temperature, a preset time of 12 hours for cooling back to the starting temperature and resting, and the time required for each temperature adjustment. Assuming that each temperature adjustment takes about 1 hour, the second time interval is 12 hours + 12 hours + 12 hours + 1 hour + 1 hour = 38 hours. Dividing the voltage difference of -3 millivolts by the second time interval of 38 hours yields the estimated self-discharge coefficient in the low-temperature region as -3 millivolts divided by 38 hours, which equals -0.0789 millivolts per hour. This value indicates that during the entire time interval from the measurement of the first open-circuit voltage to the measurement of the sixth open-circuit voltage, the open-circuit voltage of the battery under test decreases at an average rate of approximately 0.0789 millivolts per hour.

[0084] The self-discharge coefficient estimates for the high-temperature and low-temperature regions are averaged to obtain the self-discharge impact. This calculation step is designed to integrate measurement data from different temperature conditions and time periods to obtain a more stable and reliable estimate of the self-discharge rate. Specifically, the self-discharge coefficient estimate for the high-temperature region (-0.0833 mV / h) is added to the self-discharge coefficient estimate for the low-temperature region (-0.0789 mV / h), and then divided by two to obtain -0.0811 mV / h. Taking the absolute value yields the self-discharge impact of 0.0811 mV / h. The physical meaning of this self-discharge effect is the average self-discharge rate exhibited by the battery under test throughout the measurement process. Although the actual self-discharge rate of the battery may vary slightly at different temperatures, the estimated self-discharge coefficient in the high-temperature region (0.0833 mV / h) is slightly higher than the estimated self-discharge coefficient in the low-temperature region (0.0789 mV / h), reflecting the general rule that increased temperature usually accelerates electrochemical reactions, including self-discharge reactions. However, the similar values ​​indicate that the influence of temperature on the self-discharge rate is relatively small. By averaging, a representative self-discharge rate value can be obtained for subsequent time correction calculations. It should be noted that the estimated self-discharge coefficient in the low-temperature region actually includes the influence of temperature changes. However, since the voltage change caused by temperature changes is relatively small compared to the cumulative effect of self-discharge, and it is considered in conjunction with the estimated self-discharge coefficient in the high-temperature region during the averaging calculation, the final self-discharge effect can better represent the influence of the pure self-discharge effect.

[0085] Based on the self-discharge effect and the corresponding time parameters for each measurement, the target voltage deviation caused by self-discharge at each measurement point is calculated. The purpose of this calculation step is to quantify the specific value of the cumulative self-discharge effect contained in each open-circuit voltage measurement, providing an accurate correction amount for subsequent time correction. Specifically, a time reference point needs to be determined first, typically the measurement time of the first open-circuit voltage as the time zero point. Then, the time intervals of other measurements relative to this reference point are calculated, and the cumulative voltage change caused by self-discharge within this time interval is calculated based on the self-discharge effect. For the first open-circuit voltage, the measurement time is defined as the time zero point, therefore the relative time interval is zero, and the target voltage deviation is the self-discharge effect of 0.0811 millivolts per hour multiplied by zero, which equals zero millivolts. This indicates that the first open-circuit voltage, as a reference point, does not require self-discharge correction. For the second open-circuit voltage, its measurement time relative to the first open-circuit voltage measurement time includes the time between the first heating and resting periods, including approximately 1 hour of heating and a preset resting time of 12 hours at the termination temperature, totaling approximately 13 hours. The target voltage deviation is 0.0811 mV / hour multiplied by 13 hours, which equals 1.054 mV, indicating that the second open-circuit voltage includes approximately 1.054 mV of voltage reduction due to self-discharge. For the fifth open-circuit voltage, its measurement time relative to the first open-circuit voltage measurement time includes the time between the first heating and resting periods plus the time of continued resting at the termination temperature, totaling approximately 1 hour plus 12 hours plus 12 hours, which equals 25 hours. The target voltage deviation is 0.0811 mV / hour multiplied by 25 hours, which equals 2.028 mV. For the sixth open-circuit voltage, its measurement time relative to the first open-circuit voltage measurement time has gone through all the aforementioned processes plus the time for cooling back to the starting temperature and settling, which is the second time interval of 38 hours calculated above. The target voltage deviation is 0.0811 millivolts per hour multiplied by 38 hours equals 3.082 millivolts.

[0086] Time correction is performed by subtracting the corresponding target voltage deviation from the first, second, fifth, and sixth open-circuit voltages, resulting in multiple corrected open-circuit voltages. The physical meaning of this time correction is to uniformly adjust the open-circuit voltage values ​​at all measurement points to the state of charge corresponding to the time reference point, eliminating differences in self-discharge accumulation effects caused by different measurement times. This ensures that the corrected voltage values ​​accurately reflect the pure temperature effect without the interference of the time factor. Specifically, the first open-circuit voltage of 3.852 volts is subtracted from the corresponding target voltage deviation of zero millivolts to obtain the first corrected open-circuit voltage of 3.852 volts. Since the first open-circuit voltage serves as the reference point, its correction value remains unchanged. Subtracting the corresponding target voltage deviation of 1.054 millivolts from the second open-circuit voltage of 3.848 volts yields the second corrected open-circuit voltage of 3.848 volts plus 1.054 millivolts, which equals 3.849 volts. It's important to note that the target voltage deviation represents the voltage drop caused by self-discharge; therefore, this drop should be compensated for during correction, i.e., an addition operation should be performed. The second corrected open-circuit voltage of 3.849 volts represents the voltage value that should have been measured if the second open-circuit voltage measurement had been performed at zero time instead of 13 hours later, without the influence of self-discharge. Adding the corresponding target voltage deviation of 2.028 millivolts to the fifth open-circuit voltage of 3.847 volts yields the fifth corrected open-circuit voltage of 3.849 volts. Adding the corresponding target voltage deviation of 3.082 millivolts to the sixth open-circuit voltage of 3.849 volts yields the sixth corrected open-circuit voltage of 3.852 volts. Through the above time correction calculations, four corrected open-circuit voltage values ​​were successfully obtained. These corrected voltage values ​​have eliminated the effects of self-discharge accumulating over time and can be used to accurately calculate the pure temperature effect.

[0087] Furthermore, based on the temperature difference between the starting temperature and the ending temperature, and the voltage difference between the corrected open-circuit voltages at different temperatures, the temperature influence of the battery under test is calculated. Specifically, this includes: calculating the first corrected voltage difference between the corrected open-circuit voltage corresponding to the second open-circuit voltage and the corrected open-circuit voltage corresponding to the first open-circuit voltage, and calculating the first temperature difference between the ending temperature and the starting temperature; using the ratio of the first corrected voltage difference to the first temperature difference as the temperature coefficient of the heating path; calculating the second corrected voltage difference between the corrected open-circuit voltage corresponding to the sixth open-circuit voltage and the corrected open-circuit voltage corresponding to the fifth open-circuit voltage, and calculating the second temperature difference between the starting temperature and the ending temperature; using the ratio of the second corrected voltage difference to the second temperature difference as the temperature coefficient of the cooling path; and averaging the temperature coefficients of the heating path and the cooling path to obtain the temperature influence.

[0088] Specifically, the calculation involves determining the first corrected voltage difference between the corrected open-circuit voltage corresponding to the second open-circuit voltage and the corrected open-circuit voltage corresponding to the first open-circuit voltage, as well as the first temperature difference between the termination temperature and the starting temperature. This calculation focuses on the heating process experienced by the battery under test. The first open-circuit voltage was measured after standing at the initial temperature of 22°C for 12 hours, corresponding to a first corrected open-circuit voltage of 3.852 volts. The second open-circuit voltage was measured after the battery under test was heated from the initial temperature of 22°C to the termination temperature of 28°C and then stood for 12 hours, corresponding to a second corrected open-circuit voltage of 3.849 volts. Subtracting the first corrected open-circuit voltage of 3.852 volts from the second corrected open-circuit voltage of 3.849 volts yields a first corrected voltage difference of -0.003 volts, or -3 millivolts. This negative sign indicates that the open-circuit voltage decreases as the temperature increases, and the absolute value of 3 millivolts represents the voltage drop caused purely by temperature factors as the temperature rises from the initial temperature to the termination temperature along the heating path. The first temperature difference is calculated as the final temperature of 28°C minus the initial temperature of 22°C, resulting in a first temperature difference of 6°C. This temperature difference represents the magnitude of temperature change along the heating path. The calculation of the first corrected voltage difference is particularly important because both the first and second corrected open-circuit voltages have had their self-discharge accumulation effects eliminated through time correction. The first corrected open-circuit voltage of 3.852 volts is the voltage value that should be measured at the initial temperature of 22°C under conditions of zero time and no self-discharge effect. The second corrected open-circuit voltage of 3.849 volts is the voltage value that should be measured at the final temperature of 28°C under conditions of zero time and no self-discharge effect. Therefore, the difference between the two purely reflects the effect of temperature change and completely excludes interference from time or self-discharge factors.

[0089] The ratio of the first correction voltage difference to the first temperature difference is used as the heating path temperature coefficient. This heating path temperature coefficient quantitatively characterizes the response characteristics of the open-circuit voltage of the battery under test as a function of temperature during the heating process. Specifically, the first correction voltage difference of -3 mV is divided by the first temperature difference of 6 degrees Celsius, resulting in a heating path temperature coefficient of -0.5 mV per degree Celsius. The physical meaning of this negative sign is that the open-circuit voltage decreases as the temperature increases. This is a typical characteristic of lithium-ion batteries because an increase in temperature alters the thermodynamic equilibrium state of the electrode materials and the activity of ions in the electrolyte, typically leading to a decrease in the battery's equilibrium potential. The absolute value of the heating path temperature coefficient, 0.5 mV per degree Celsius, indicates that during the heating process, the open-circuit voltage of the battery under test decreases by approximately 0.5 mV for every 1 degree Celsius increase in temperature. This value accurately reflects the influence of temperature on the open-circuit voltage along the heating path. The temperature coefficient of the heating path is calculated based on time-corrected open-circuit voltage data, ensuring that the coefficient is completely unaffected by the self-discharge effect and can truly characterize the pure temperature effect. Its measurement accuracy mainly depends on the accuracy of temperature control and the precision of open-circuit voltage measurement. In this embodiment, under the conditions that the temperature control accuracy is ±0.5 degrees Celsius and the voltage measurement accuracy is ±0.1 millivolts, the relative measurement error of the temperature coefficient of the heating path can be controlled within five percent.

[0090] The calculation steps focus on the cooling process of the battery under test. The fifth open-circuit voltage was measured after the battery was left to stand at the final temperature of 28°C for 12 hours, resulting in a fifth corrected open-circuit voltage of 3.849 volts. The sixth open-circuit voltage was measured after the battery was cooled from the final temperature of 28°C back to the initial temperature of 22°C and left to stand for 12 hours, resulting in a sixth corrected open-circuit voltage of 3.852 volts. Subtracting the fifth corrected open-circuit voltage of 3.849 volts from the sixth corrected open-circuit voltage of 3.852 volts yields a second corrected voltage difference of +0.003 volts, or +3 millivolts. This positive sign indicates that the open-circuit voltage increases as the temperature decreases, and the absolute value of 3 millivolts represents the voltage increase caused purely by temperature factors as the temperature decreases from the final temperature to the initial temperature along the cooling path. The second temperature difference is calculated by subtracting the final temperature of 28°C from the initial temperature of 22°C, resulting in a negative temperature difference of 6°C. This negative temperature difference represents the direction and magnitude of temperature change along the cooling path. The calculation of the second corrected voltage difference is also based on the time-corrected open-circuit voltage data. The fifth corrected open-circuit voltage of 3.849 volts represents the voltage value that should be measured at the final temperature of 28°C under the condition that there is no self-discharge effect at the zero time point. The sixth corrected open-circuit voltage of 3.852 volts represents the voltage value that should be measured at the initial temperature of 22°C under the condition that there is no self-discharge effect at the zero time point. The difference between the two purely reflects the influence of temperature change on the open-circuit voltage during the cooling process.

[0091] The ratio of the second correction voltage difference to the second temperature difference is used as the cooling path temperature coefficient. This cooling path temperature coefficient quantitatively characterizes the response characteristics of the open-circuit voltage of the battery under test during the cooling process. Specifically, the second correction voltage difference of +3 mV is divided by the second temperature difference of -6 degrees Celsius, resulting in a cooling path temperature coefficient of -0.5 mV per degree Celsius. The negative sign in this calculation result comes from dividing a positive voltage difference by a negative temperature difference; the physical meaning remains that the open-circuit voltage decreases as the temperature increases, or equivalently, it can be expressed as the open-circuit voltage increases as the temperature decreases, consistent with the physical law of the heating path. The absolute value of the cooling path temperature coefficient, 0.5 mV per degree Celsius, indicates that during the cooling process, the open-circuit voltage of the battery under test increases by approximately 0.5 mV for every 1 degree Celsius decrease in temperature, or equivalently, decreases by approximately 0.5 mV for every 1 degree Celsius increase in temperature. This value accurately reflects the influence of temperature on the open-circuit voltage along the cooling path. By comparing the temperature coefficients of the heating path and the cooling path, it can be found that the absolute values ​​of both are 0.5 mV per degree Celsius and have the same sign. This indicates that the open-circuit voltage of the battery under test exhibits good consistency and reversibility in the heating and cooling processes, without obvious hysteresis or path dependence. This is an important indicator of good battery performance, suggesting that the electrochemical reaction inside the battery can quickly respond to temperature changes and reach a new equilibrium state.

[0092] The temperature effect is obtained by averaging the temperature coefficients of the heating and cooling paths. This averaging calculation aims to synthesize the measurement results from both paths, resulting in a more comprehensive, stable, and reliable value for the temperature effect. This value more accurately represents the overall characteristics of the open-circuit voltage response of the battery under test when the temperature changes. Adding the heating path temperature coefficient (-0.5 mV / °C) to the cooling path temperature coefficient (-0.5 mV / °C) and dividing by two yields a temperature effect of -0.5 mV / °C. In practical applications, the absolute value is usually taken, and the negative sign is omitted, expressing the temperature effect as 0.5 mV / °C. This explicitly states that this is the decrease in open-circuit voltage per degree Celsius as the temperature increases, or equivalently, a temperature compensation coefficient of 0.5 mV / °C. The physical meaning of this temperature effect is that, regardless of whether the battery under test undergoes a heating or cooling process, the relationship between the open-circuit voltage and temperature follows the same linear law. That is, for every 1 degree Celsius change in temperature, the open-circuit voltage changes by 0.5 millivolts. This value does not include the influence of self-discharge or time factors at all, and is a pure temperature effect parameter.

[0093] The temperature effect obtained through the above calculation method can be directly applied to the open-circuit voltage temperature compensation algorithm in the battery production process. When measuring the open-circuit voltage of a battery at a non-standard temperature, the equivalent voltage value corresponding to the open-circuit voltage at the standard reference temperature can be accurately calculated based on the difference between the actual measured temperature and the standard reference temperature, as well as the temperature effect. This enables unified comparison and accurate grading of measurement results under different temperature conditions. For example, if the standard reference temperature is set to 25 degrees Celsius, and a battery measures an open-circuit voltage of 3.845 volts at 30 degrees Celsius, then the equivalent voltage corresponding to this voltage value at the standard reference temperature of 25 degrees Celsius is 3.845 volts plus 5 degrees Celsius multiplied by 0.5 millivolts per degree Celsius, which equals 3.8475 volts. This temperature compensation calculation can eliminate the influence of measurement temperature deviation on the open-circuit voltage measurement results, ensuring the accuracy and consistency of battery grading.

[0094] To illustrate this application more clearly, a specific embodiment is given. It is assumed that the battery under test is a lithium iron phosphate battery with an initial temperature of 22°C, an ending temperature of 28°C, and a preset time of 12 hours. Through previous experimental calibration, the slope of the open circuit voltage curve at 50% SOC is -50mV / %, and the hysteresis difference is 10mV. The battery under test was scanned for the first time, and the first open-circuit voltage was measured to be 3.957V and the second open-circuit voltage to be 3.930V. Based on the calculation formula above, the current expected voltage error was calculated to be 23mV. The maximum voltage error threshold was set to 10mV. Since the current expected voltage error of 23mV > 10mV, the state reset and difference method path was selected. The battery under test was fully discharged to 2.5V and then charged to 50% SOC. The third open-circuit voltage was then measured to be 3.933V and the fourth open-circuit voltage to be 3.953V. The voltage difference due to temperature rise was 27mV, and the voltage difference due to temperature drop was 20mV. The final temperature effect was (27+20) / 2 / (28-22) = 3.92 mV / ℃, and the self-discharge effect was (27-20) / 2 = 3.5mV (within 12 hours).

[0095] This application embodiment also provides a battery open-circuit voltage temperature compensation measurement device based on bidirectional temperature scanning. The device includes a first measurement unit, a processing unit, a second measurement unit, and a calculation unit. The first measurement unit places the battery under test in a preset state of charge in an environment at an initial temperature for a preset time and measures the first open-circuit voltage; then adjusts the ambient temperature of the battery under test to a final temperature and places it in a preset time to measure the second open-circuit voltage. The processing unit acquires the open-circuit voltage curve of the battery under test at a standard temperature, extracts the curve slope corresponding to the preset state of charge, and retrieves the hysteresis difference and high-temperature aging value corresponding to the material of the battery under test; calculates the curve slope, hysteresis difference, and high-temperature aging value to obtain the current expected voltage error; and compares the current expected voltage error with a maximum voltage error threshold. The second measurement unit, if the current expected voltage error is greater than the maximum voltage error threshold, then... The battery execution state is reset. The reset battery under test is placed at the termination temperature and left to stand for a preset time. The third open-circuit voltage is measured. The ambient temperature of the battery under test is adjusted to the starting temperature and left to stand for a preset time. The fourth open-circuit voltage is measured. If the current expected voltage error is less than or equal to the maximum voltage error threshold, the continuous testing state of the battery under test is maintained. The battery is left to stand at the termination temperature for a preset time and the fifth open-circuit voltage is measured. The ambient temperature of the battery under test is adjusted to the starting temperature and left to stand for a preset time. The sixth open-circuit voltage is measured. The calculation unit calculates the self-discharge effect and temperature effect of the battery under test by using the difference method on the first, second, third, and fourth open-circuit voltages. The slope averaging method is used to calculate the self-discharge effect and temperature effect of the battery under test on the first, second, fifth, and sixth open-circuit voltages.

[0096] In one possible implementation, the calculation unit is used to subtract the second open-circuit voltage from the first open-circuit voltage to obtain the heating voltage difference; subtract the third open-circuit voltage from the fourth open-circuit voltage to obtain the cooling voltage difference; add the heating voltage difference and the cooling voltage difference and divide by two to obtain the temperature influence of the battery under test; subtract the cooling voltage difference from the heating voltage difference and divide by two to obtain the self-discharge influence of the battery under test.

[0097] In one possible implementation, the calculation unit is used to divide the difference between the fifth open-circuit voltage and the second open-circuit voltage by a first time interval to obtain an estimated value of the self-discharge coefficient in the high-temperature region, where the first time interval is the time interval between the fifth open-circuit voltage and the second open-circuit voltage; divide the difference between the sixth open-circuit voltage and the first open-circuit voltage by a second time interval to obtain an estimated value of the self-discharge coefficient in the low-temperature region, where the second time interval is the time interval between the sixth open-circuit voltage and the first open-circuit voltage; average the estimated value of the self-discharge coefficient in the high-temperature region and the estimated value of the self-discharge coefficient in the low-temperature region to obtain the self-discharge influence; calculate the target voltage deviation caused by self-discharge at each measurement point according to the self-discharge influence and the time parameters corresponding to each measurement, and subtract the corresponding target voltage deviation from the first open-circuit voltage, the second open-circuit voltage, the fifth open-circuit voltage and the sixth open-circuit voltage for time correction to obtain multiple corrected open-circuit voltages; calculate the temperature influence of the battery under test based on the temperature difference between the starting temperature and the ending temperature, and the voltage difference between the corresponding corrected open-circuit voltages at different temperatures.

[0098] In one possible implementation, the calculation unit is used to calculate the first corrected voltage difference between the corrected open-circuit voltage corresponding to the second open-circuit voltage and the corrected open-circuit voltage corresponding to the first open-circuit voltage, and to calculate the first temperature difference between the termination temperature and the starting temperature, and to use the ratio of the first corrected voltage difference to the first temperature difference as the temperature coefficient of the heating path; to calculate the second corrected voltage difference between the corrected open-circuit voltage corresponding to the sixth open-circuit voltage and the corrected open-circuit voltage corresponding to the fifth open-circuit voltage, and to calculate the second temperature difference between the starting temperature and the termination temperature, and to use the ratio of the second corrected voltage difference to the second temperature difference as the temperature coefficient of the cooling path; and to average the temperature coefficient of the heating path and the temperature coefficient of the cooling path to obtain the temperature influence amount.

[0099] In one possible implementation, the processing unit is used to acquire the reversible self-discharge rate of the battery under test at the test temperature, the estimated time spent at the target temperature, and the hysteresis activation coefficient; add the reversible self-discharge rate to the high-temperature aging value to obtain the total capacity loss rate, wherein the high-temperature aging value is the irreversible aging rate calculated based on the Arrhenius equation; multiply the total capacity loss rate, the estimated time, and the absolute value of the curve slope to obtain a first voltage error term; multiply the hysteresis activation coefficient and the hysteresis difference to obtain a second voltage error term; and add the first voltage error term and the second voltage error term to obtain the current expected voltage error.

[0100] In one possible implementation, the processing unit is used to obtain the absolute temperature difference between the initial temperature and the target temperature; divide the absolute temperature difference by the reference temperature span to obtain the temperature activation factor; obtain the estimated time for the battery under test to stand at the target temperature, and divide the estimated time by the hysteresis relaxation time constant to obtain the time ratio; calculate the power function value of the natural constant with the negative of the time ratio as the exponent, and subtract the power function value from 1 to obtain the time relaxation factor; multiply the temperature activation factor and the time relaxation factor to obtain the hysteresis activation coefficient.

[0101] In one possible implementation, the processing unit is used to acquire first voltage and state of charge (SOC) data of the battery under test during discharge at a standard temperature; to charge the battery under test at a constant current until the charging cutoff condition is met, and acquire second voltage and SOC data during the charging process; to calculate the arithmetic mean of the first voltage and the second voltage under the same SOC, and to fit and generate an open-circuit voltage curve at the standard temperature based on the arithmetic mean corresponding to each SOC point; to determine a target voltage point corresponding to a preset SOC on the open-circuit voltage curve; to select a first SOC point and a second SOC point within a preset neighborhood of the preset SOC, and to acquire the first voltage value corresponding to the first SOC point and the second voltage value corresponding to the second SOC point from the open-circuit voltage curve, respectively; and to divide the difference between the first voltage value and the second voltage value by the difference between the first SOC point and the second SOC point to obtain the slope of the curve corresponding to the preset SOC.

[0102] It should be noted that the above embodiments of the apparatus are only illustrated by the division of the above functional modules. In practical applications, the above functions can be assigned to different functional modules as needed, that is, the internal structure of the device can be divided into different functional modules to complete all or part of the functions described above. In addition, the apparatus and method embodiments provided in the above embodiments belong to the same concept, and the specific implementation process can be found in the method embodiments, which will not be repeated here.

[0103] This application also discloses an electronic device. (See reference...) Figure 4 , Figure 4 This application provides a schematic diagram of the structure of an electronic device. The electronic device 400 may include: at least one processor 401, at least one network interface 404, a user interface 403, a memory 402, and at least one communication bus 405.

[0104] The communication bus 405 is used to enable communication between these components.

[0105] The user interface 403 may include a display screen and a camera. Optionally, the user interface 403 may also include a standard wired interface and a wireless interface.

[0106] The network interface 404 may optionally include a standard wired interface or a wireless interface (such as a Wi-Fi interface).

[0107] The processor 401 may include one or more processing cores. The processor 401 connects to various parts of the server using various interfaces and lines, and performs various server functions and processes data by running or executing instructions, programs, code sets, or instruction sets stored in memory 402, and by calling data stored in memory 402. Optionally, the processor 401 may be implemented using at least one hardware form of Digital Signal Processing (DSP), Field-Programmable Gate Array (FPGA), or Programmable Logic Array (PLA). The processor 401 may integrate one or a combination of several of the following: Central Processing Unit (CPU), Graphics Processing Unit (GPU), and modem. The CPU primarily handles the operating system, user interface, and application requests; the GPU is responsible for rendering and drawing the content required for display; and the modem handles wireless communication. It is understood that the modem may also be implemented as a separate chip without being integrated into the processor 401.

[0108] The memory 402 may include random access memory (RAM) or read-only memory. Optionally, the memory 402 may include a non-transitory computer-readable storage medium. The memory 402 can be used to store instructions, programs, code, code sets, or instruction sets. The memory 402 may include a program storage area and a data storage area. The program storage area may store instructions for implementing an operating system, instructions for at least one function (such as touch functionality, sound playback functionality, image playback functionality, etc.), instructions for implementing the various method embodiments described above, etc. The data storage area may store data involved in the various method embodiments described above. Optionally, the memory 402 may also be at least one storage device located remotely from the aforementioned processor 401.

[0109] like Figure 4As shown, the memory 402, which serves as a computer storage medium, may include an operating system, a network communication module, a user interface module, and an application program for measuring the open-circuit voltage temperature compensation of a battery based on bidirectional temperature scanning.

[0110] exist Figure 4 In the electronic device 400 shown, the user interface 403 is mainly used to provide an input interface for the user and to obtain the user input data; while the processor 401 can be used to call the application program stored in the memory 402 for battery open circuit voltage temperature compensation measurement based on bidirectional temperature scanning. When executed by one or more processors, the electronic device performs one or more of the methods described in the above embodiments.

[0111] It should be noted that, for the sake of simplicity, the foregoing method embodiments are all described as a series of actions. However, those skilled in the art should understand that this application is not limited to the described order of actions, as some steps may be performed in other orders or simultaneously according to this application. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions and modules involved are not necessarily essential to this application.

[0112] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0113] In the several embodiments provided in this application, it should be understood that the disclosed apparatus can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the displayed or discussed mutual couplings, direct couplings, or communication connections may be through some service interfaces; indirect couplings or communication connections between devices or units may be electrical or other forms.

[0114] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0115] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0116] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage device (CMD). Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a memory and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned memory includes various media capable of storing program code, such as USB flash drives, portable hard drives, magnetic disks, or optical disks.

[0117] The foregoing description is merely an exemplary embodiment of this disclosure and should not be construed as limiting the scope of this disclosure. Any equivalent changes and modifications made in accordance with the teachings of this disclosure shall still fall within the scope of this disclosure. Those skilled in the art will readily conceive of other embodiments of this disclosure upon considering the specification and practical application disclosed herein. This application is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not described in this disclosure.

Claims

1. A method for measuring the open-circuit voltage temperature compensation of a battery based on bidirectional temperature scanning, characterized in that, The method includes: The battery under test is placed in an initial temperature environment under a preset state of charge and left to stand for a preset time. The first open-circuit voltage is then measured. The ambient temperature of the battery under test is adjusted to the termination temperature, and the battery is left to stand for the preset time to measure the second open-circuit voltage. Obtain the open-circuit voltage curve of the battery under test at a standard temperature, extract the slope of the curve corresponding to the preset state of charge, and retrieve the hysteresis difference and high-temperature aging value corresponding to the material of the battery under test. The current expected voltage error is obtained by calculating the slope of the curve, the hysteresis difference, and the high-temperature aging value. Compare the current expected voltage error with the maximum voltage error threshold; If the current expected voltage error is greater than the maximum voltage error threshold, the state of the battery under test is reset, the reset battery under test is placed at the termination temperature and left to stand for the preset time, the third open circuit voltage is measured, the ambient temperature of the battery under test is adjusted to the starting temperature and left to stand for the preset time, and the fourth open circuit voltage is measured. The self-discharge effect and temperature effect of the battery under test are obtained by calculating the difference between the first open-circuit voltage, the second open-circuit voltage, the third open-circuit voltage and the fourth open-circuit voltage using the difference method. If the current expected voltage error is less than or equal to the maximum voltage error threshold, then the continuous testing state of the battery under test is maintained, and the battery is left to stand for the preset time at the termination temperature to measure the fifth open circuit voltage. The ambient temperature of the battery under test is adjusted to the starting temperature and left to stand for the preset time to measure the sixth open circuit voltage. The self-discharge effect and temperature effect of the battery under test are obtained by calculating the first open-circuit voltage, the second open-circuit voltage, the fifth open-circuit voltage, and the sixth open-circuit voltage using the slope averaging method.

2. The method according to claim 1, characterized in that, The step of calculating the self-discharge effect and temperature effect of the battery under test by performing a difference method on the first open-circuit voltage, the second open-circuit voltage, the third open-circuit voltage, and the fourth open-circuit voltage specifically includes: Subtract the second open-circuit voltage from the first open-circuit voltage to obtain the heating voltage difference; Subtracting the third open-circuit voltage from the fourth open-circuit voltage yields the cooling voltage difference. Add the heating voltage difference and the cooling voltage difference, then divide by two to obtain the temperature influence of the battery under test; Subtracting the cooling voltage difference from the heating voltage difference and then dividing by two yields the self-discharge effect of the battery under test.

3. The method according to claim 1, characterized in that, The calculation of the self-discharge effect and temperature effect of the battery under test by applying the slope averaging method to the first open-circuit voltage, the second open-circuit voltage, the fifth open-circuit voltage, and the sixth open-circuit voltage specifically includes: Divide the difference between the fifth open-circuit voltage and the second open-circuit voltage by the first time interval to obtain the estimated value of the self-discharge coefficient in the high-temperature region. The first time interval is the time interval between the fifth open-circuit voltage and the second open-circuit voltage. Divide the difference between the sixth open-circuit voltage and the first open-circuit voltage by the second time interval to obtain the estimated value of the self-discharge coefficient in the low-temperature region. The second time interval is the time interval between the sixth open-circuit voltage and the first open-circuit voltage. The self-discharge influence quantity is obtained by averaging the estimated self-discharge coefficient in the high-temperature region and the estimated self-discharge coefficient in the low-temperature region. Based on the self-discharge effect and the time parameters corresponding to each measurement, the target voltage deviation caused by self-discharge at each measurement point is calculated, and the corresponding target voltage deviation is subtracted from the first open-circuit voltage, the second open-circuit voltage, the fifth open-circuit voltage and the sixth open-circuit voltage for time correction to obtain multiple corrected open-circuit voltages. Based on the temperature difference between the starting temperature and the ending temperature, and the voltage difference between the corrected open-circuit voltages at different temperatures, the temperature influence of the battery under test is calculated.

4. The method according to claim 3, characterized in that, The temperature influence of the battery under test is calculated based on the temperature difference between the starting temperature and the ending temperature, and the voltage difference between the corrected open-circuit voltages at different temperatures. Specifically, this includes: Calculate the first corrected voltage difference between the corrected open-circuit voltage corresponding to the second open-circuit voltage and the corrected open-circuit voltage corresponding to the first open-circuit voltage, and calculate the first temperature difference between the termination temperature and the starting temperature. Use the ratio of the first corrected voltage difference to the first temperature difference as the temperature coefficient of the heating path. Calculate the second corrected voltage difference between the corrected open-circuit voltage corresponding to the sixth open-circuit voltage and the corrected open-circuit voltage corresponding to the fifth open-circuit voltage, and calculate the second temperature difference between the starting temperature and the ending temperature. Use the ratio of the second corrected voltage difference to the second temperature difference as the cooling path temperature coefficient. The temperature influence is obtained by averaging the temperature coefficient of the heating path and the temperature coefficient of the cooling path.

5. The method according to claim 1, characterized in that, The calculation of the curve slope, the hysteresis difference, and the high-temperature aging value to obtain the current expected voltage error specifically includes: The reversible self-discharge rate of the battery under test at the test temperature, the estimated time of residence at the target temperature, and the hysteresis activation coefficient are obtained. The reversible self-discharge rate is added to the high-temperature aging value to obtain the total capacity loss rate, wherein the high-temperature aging value is the irreversible aging rate calculated based on the Arrhenius equation. The first voltage error term is obtained by multiplying the total capacity loss rate, the estimated time, and the absolute value of the curve slope together. The second voltage error term is obtained by multiplying the hysteresis activation coefficient and the hysteresis difference. The first voltage error term is added to the second voltage error term to obtain the current expected voltage error.

6. The method according to claim 5, characterized in that, The process of obtaining the hysteresis activation coefficient of the battery under test specifically includes: Obtain the absolute temperature difference between the starting temperature and the target temperature; Divide the absolute temperature difference by the reference temperature span to obtain the temperature activation factor; The estimated time for the battery under test to be placed at the target temperature is obtained, and the estimated time is divided by the hysteresis relaxation time constant to obtain the time ratio. Calculate the power function value of the natural constant with the negative of the time ratio as the exponent, and subtract the power function value from 1 to obtain the time relaxation factor; The hysteresis activation coefficient is obtained by multiplying the temperature activation factor by the time relaxation factor.

7. The method according to claim 1, characterized in that, The process of obtaining the open-circuit voltage curve of the battery under test at a standard temperature and extracting the slope of the curve corresponding to the preset state of charge specifically includes: Acquire the first voltage and state of charge data of the battery under test during the discharge process at the standard temperature; The battery under test is charged at a constant current until the charging cutoff condition is met, and the second voltage and state of charge data during the charging process are acquired. Calculate the arithmetic mean of the first voltage and the second voltage under the same state of charge, and generate the open-circuit voltage curve at the standard temperature based on the arithmetic mean corresponding to each state of charge point; Determine the target voltage point corresponding to the preset state of charge on the open-circuit voltage curve; Within a preset neighborhood of the preset state of charge, a first state of charge point and a second state of charge point are selected, and the first voltage value corresponding to the first state of charge point and the second voltage value corresponding to the second state of charge point are obtained from the open circuit voltage curve, respectively. The slope of the curve corresponding to the preset state of charge is obtained by dividing the difference between the first voltage value and the second voltage value by the difference between the first state of charge point and the second state of charge point.

8. A battery open-circuit voltage temperature compensation measurement device based on bidirectional temperature scanning, characterized in that, The device includes a first measurement unit, a processing unit, a second measurement unit, and a calculation unit. The first measuring unit places the battery under test in a preset charged state in an environment at an initial temperature for a preset time and measures the first open-circuit voltage; then adjusts the ambient temperature of the battery under test to a final temperature and places it in a preset time to measure the second open-circuit voltage. The processing unit acquires the open-circuit voltage curve of the battery under test at a standard temperature, extracts the curve slope corresponding to the preset state of charge, and retrieves the hysteresis difference and high-temperature aging value corresponding to the material of the battery under test; calculates the curve slope, the hysteresis difference, and the high-temperature aging value to obtain the current expected voltage error; and compares the current expected voltage error with the maximum voltage error threshold. The second measurement unit, if the current expected voltage error is greater than the maximum voltage error threshold, performs a state reset on the battery under test, places the reset battery under test at the termination temperature for the preset time, measures the third open-circuit voltage, adjusts the ambient temperature of the battery under test to the starting temperature and places it for the preset time, measures the fourth open-circuit voltage; if the current expected voltage error is less than or equal to the maximum voltage error threshold, maintains the continuous testing state of the battery under test, continues to place it at the termination temperature for the preset time, measures the fifth open-circuit voltage, and adjusts the ambient temperature of the battery under test to the starting temperature and places it for the preset time, measures the sixth open-circuit voltage; The calculation unit performs a difference method on the first open-circuit voltage, the second open-circuit voltage, the third open-circuit voltage, and the fourth open-circuit voltage to obtain the self-discharge effect and the temperature effect of the battery under test; and performs a slope averaging method on the first open-circuit voltage, the second open-circuit voltage, the fifth open-circuit voltage, and the sixth open-circuit voltage to obtain the self-discharge effect and the temperature effect of the battery under test.

9. An electronic device, characterized in that, The device includes a processor, a memory, a user interface, and a network interface. The memory is used to store instructions, the user interface and the network interface are used to communicate with other devices, and the processor is used to execute the instructions stored in the memory to cause the electronic device to perform the method as described in any one of claims 1-7.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores instructions that, when executed, perform the method as described in any one of claims 1-7.

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