Method for testing peak current of power battery

Abstract

The invention discloses a method for testing the peak current of a power battery. The method comprises the following steps: S1, determining the actual capacity of a to-be-tested battery; s2, determining test conditions of the to-be-tested battery; s3, testing peak current; under the test condition, based on a plurality of preset reference current values, carrying out peak current test with the maximum value of the target pulse duration to obtain a plurality of actually measured pulse currents, sampling and recording a pulse whole-process voltage value, and intercepting to obtain an actually measured cut-off voltage corresponding to each pulse duration node; s4, calculating theoretical peak current; outputting measured data obtained by performing peak current testing on the same pulse time length node under different reference current values as a group of theoretical data, and calculating theoretical peak current under each pulse time length node based on the theoretical data of each pulse time length node; the actually measured data comprises actually measured cut-off voltage and actually measured pulse current; and S5, performing pulse actual measurement verification on the theoretical peak current.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power battery detection, in particular to a test method for peak current of a power battery. BACKGROUND

[0002] In the field of new energy vehicles, the peak current parameter of a power lithium ion battery is crucial, which directly affects the power performance of the battery, BMS parameter calibration and user experience. The core application scenarios of this parameter include vehicle sudden acceleration and climbing, regenerative braking energy recovery, low-temperature cold start, super-fast charging, etc.

[0003] The existing test method in the industry is usually a test current method, which randomly selects a current as an initial current for testing. When the voltage of the battery does not reach the cut-off voltage or exceeds the voltage threshold after each test, the current is increased or decreased for retesting until the voltage of the battery reaches the cut-off voltage, and the current at this time is the peak current. This test method is highly accurate but usually requires a huge amount of manpower and time, has low test efficiency, and seriously affects the project development cycle.

[0004] Another invention patent application with publication number CN115356644A discloses a peak current test method, which first obtains an initial test current by constant voltage charging or discharging at a target pulse length, and then iterates the pulse continuously based on the initial test current value as the reference value until the cut-off voltage is exceeded. The corresponding current value is the peak current. In this test method, the pulse length is not controlled, and the current value less than the target pulse length is taken as the peak current, resulting in a higher test result than the actual value, low test accuracy, and the need for repeated iterative pulses in the test process, which does not have a significant advantage in test cycle. SUMMARY

[0005] To solve the above problems, the present application provides a test method for peak current of a power battery, which is based on a preset reference current value for pulse, and the theoretical peak current is fitted through the approximate linear relationship between voltage and pulse current value, and the theoretical peak current is verified, which has high test accuracy and short test cycle.

[0006] In a first aspect, the present application provides a test method for peak current of a power battery, which comprises: S1, determining the actual capacity of the battery to be tested; S2, determining the test conditions of the battery to be tested; The test conditions include variable conditions and parameter conditions, the variable conditions include: target electric quantity, target pulse duration, target temperature; the parameter conditions include cutoff voltage, the influence condition of the cutoff voltage includes the target temperature, and the target temperature is an ambient temperature; and the target pulse duration includes a plurality of pulse duration nodes. S3, peak current test; Under the test conditions, peak current tests are respectively performed on the maximum value of the target pulse duration based on a plurality of preset reference current values, a plurality of measured pulse currents are obtained, voltage values in a whole pulse process are recorded, and measured cutoff voltages corresponding to each pulse duration node are obtained by intercepting. S4, calculation of theoretical peak current; The measured data obtained by performing peak current tests on the same pulse duration node under different reference current values are output as a set of theoretical data, and the theoretical peak current under each pulse duration node is calculated based on the theoretical data of each pulse duration node; the measured data include measured cutoff voltages and measured pulse currents. S5, pulse measurement verification of theoretical peak current; The theoretical peak current under each pulse duration node is brought into pulse measurement verification, pulse test is performed on each pulse duration node based on the theoretical peak current corresponding to each pulse duration node, and end voltage values are recorded; if the end voltage values are within the cutoff voltage range corresponding to the corresponding pulse duration node, the theoretical peak current is effective.

[0007] Preferably, the influence condition of the cutoff voltage is the ambient temperature of the battery to be tested, and the cutoff voltage is a cutoff voltage of the battery to be tested measured at the target temperature.

[0008] Preferably, step S1 specifically includes: S1-1. Discharge at 1 / 3C~1C constant current to a cutoff voltage U0 at room temperature, and stand for a time t1; S1-2. Charge at 1 / 3C~1C constant current to a terminal voltage U1 at room temperature, and then charge at constant voltage until the charging current drops to 0.05C, and stop charging, and stand for a time t1; S1-3. Repeat steps S1-1 to S1-2 N times, and when the range of discharge capacities of consecutive n times is less than a preset value of a rated capacity, take the average of the experimental results of the consecutive n times as the actual capacity at room temperature; Wherein, the preset value is a first percentage, and the first percentage < 3%; N and n are positive integers, and N > 5 and n ≥ 3; and t1 is 60 min.

[0009] Preferably, the peak current test includes a charging test and a discharging test, the pulse actual test verification includes a charging actual test verification and a discharging actual test verification; the target pulse duration includes a first pulse duration node, a second pulse duration node, a third pulse duration node, a first reference current value, a second reference current value, and a third reference current value.

[0010] Preferably, during the discharging test, step S3 specifically includes: S3-1. Discharge at a constant current of 1 / 3C~1C to a target electric quantity at normal temperature; S3-2. Adjust the target temperature T of the test equipment oven and stand for a time t2; S3-3. Discharge at a constant current I1 to the maximum value of the target pulse duration, obtain the actual pulse current I1, record the pulse capacity Q1 discharged at this step, sample and record the voltage value in the whole process of the pulse, and intercept the actual cut-off voltages V1, V2, and V3 corresponding to the three pulse duration nodes; S3-4. Stand for a time t2, depolarize, charge to Q1 at a constant current I4, and return to the target electric quantity; after returning to the SOC, stand for a time t2, and depolarize; S3-5. Discharge at a constant current I2 to the maximum value of the target pulse duration, obtain the actual pulse current I2, record the pulse capacity Q2 discharged at this step, sample and record the voltage value in the whole process of the pulse, and intercept the actual cut-off voltages V4, V5, and V6 corresponding to the three pulse duration nodes; S3-6. Stand for a time t2, depolarize, charge to Q2 at a constant current I4, and return to the target electric quantity; after returning to the SOC, stand for a time t2, and depolarize; S3-7. Discharge at a constant current I3 to the maximum value of the target pulse duration, obtain the actual pulse current I3, record the pulse capacity Q3 discharged at this step, sample and record the voltage value in the whole process of the pulse, and intercept the actual cut-off voltages V7, V8, and V9 corresponding to the three pulse duration nodes; S3-8. Stand for a time t2, depolarize, charge to Q3 at a constant current I4, and return to the target electric quantity; after returning to the SOC, stand for a time t2, and depolarize; I1 is the first current reference value, I2 is the second current reference value, and I3 is the third current reference value; when the target temperature is 25℃, t2=60min; when the target temperature is greater than 0℃, t2=120min; and when the target temperature is less than or equal to 0℃, t2=720min; When the target temperature is less than or equal to 0℃, I4=0.05C; and when the target temperature is greater than 0℃, I4=1 / 3C.

[0011] Preferably, during the discharging actual test verification, step S5 specifically includes: S5-1. Discharge to the first pulse duration node at a theoretical I1 constant current, and record the pulse capacity Q4 of the discharge in this step and the corresponding terminal voltage value V10; S5-2. After standing for a time t2, charge to Q4 at a constant current I4 after depolarization, and return to the target capacity; after returning to the SOC, stand for a time t2, and depolarize; S5-3. Discharge to the second pulse duration node at a theoretical I2 constant current, and record the pulse capacity Q5 of the discharge in this step and the corresponding terminal voltage value V11; S5-4. After standing for a time t2, charge to Q5 at a constant current I4 after depolarization, and return to the target capacity; after returning to the SOC, stand for a time t2, and depolarize; S5-5. Discharge to the third pulse duration node at a theoretical I3 constant current, and record the terminal voltage value V12.

[0012] Preferably, step S5 further comprises: obtaining the corresponding cutoff voltage based on the target temperature; when any one of the V10, V11, and V12 is obtained, determining whether it matches the cutoff voltage: if it matches, the theoretical peak current is valid; if it does not match, the theoretical peak current is invalid; the cutoff voltage is a range parameter, and when the terminal voltage value in step S5 is within the range of the cutoff voltage, it matches; otherwise, it does not match.

[0013] Preferably, in step S4, the theoretical peak current at each pulse duration node is calculated based on the theoretical data of each pulse duration node, specifically comprising S4-1. Obtain the theoretical data of the first pulse duration node, the theoretical data comprising a first data point composed of a first reference current value for peak current testing and a measured pulse current and a measured cutoff voltage, a second data point composed of a second reference current value for peak current testing and a measured pulse current and a measured cutoff voltage, and a third data point composed of a third reference current value for peak current testing and a measured pulse current and a measured cutoff voltage; S4-2. Establish a first coordinate system with the measured pulse current as the abscissa and the measured cutoff voltage as the ordinate, and fit a first curve in the first coordinate system according to the theoretical data, the first curve being a peak current function curve corresponding to the first pulse duration node of the battery to be tested under the test conditions; S4-3. Repeat steps S4-1 to S4-2 to obtain the peak current function curves corresponding to other pulse duration nodes of the battery to be tested under the test conditions; S4-4. Calculate the theoretical peak current of each pulse duration node based on the peak current function curve corresponding to each pulse duration node.

[0014] Preferably, the selection range of the at least three groups of reference currents is selected, and the first reference current value, the second reference current value and the third reference current value are determined before the peak current test. The selection range of the three groups of reference currents is specifically a first reference range, a second reference range and a third reference range, and the pull range between the first reference range, the second reference range and the third reference range is pulled, so that three data points in a group of theoretical data obtained by performing peak current tests on the same pulse duration node based on the three reference current values are uniformly distributed on the peak current function curve. The first reference current value is determined based on the first reference range, the second reference current value is determined based on the second reference range, and the third reference current value is determined based on the third reference range.

[0015] Preferably, step S2 specifically comprises: The target electric quantity is a percentage of the SOC value of the remaining electric quantity of the battery to be tested, the target electric quantity is divided into a plurality of percentages of the SOC value based on the actual capacity, and an arbitrary percentage of the SOC value is selected when the test condition is determined. The target temperature is divided into a plurality of gradient values based on the ambient temperature, and an arbitrary gradient value is selected when the test condition is determined. The target pulse duration includes a plurality of pulse duration nodes, the maximum pulse duration node is determined first when the test condition is determined, and other pulse duration nodes are selected in turn based on the maximum pulse duration node. The cut-off voltage is determined based on each gradient value of the target temperature to obtain the cut-off voltage of the battery to be tested at each gradient value, and the corresponding cut-off voltage is retrieved based on the selected target temperature when the test condition is determined.

[0016] The beneficial effects of the present application are: The present application is a test method for the peak current of a power battery, which performs pulse through a given reference current value, fits the theoretical peak current based on the approximate linear relationship between the voltage and the pulse current value, and verifies the theoretical peak current by actual measurement to ensure the accuracy of the test result. Compared with the conventional test current method, it has relatively clear periodicity and obvious overall test period advantage.

[0017] The present application tests the maximum value of the target pulse duration, intercepts the approximate linear relationship between the voltage value and the pulse current of different target pulse duration nodes, and can simultaneously fit the peak current values of multiple pulse duration nodes, thereby greatly reducing the test period.

[0018] The application can be applied to peak current testing of a battery in a charging and discharging stage, and can freely configure a pulse duration node. By adjusting a cutting point of measured data, peak current testing of different pulse duration nodes can be realized. BRIEF DESCRIPTION OF DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required to be used in the embodiments will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort.

[0020] Figure 1 A flowchart of a testing method of a peak current of a power battery provided by the embodiments of the present application; Figure 2 A schematic diagram of a linear relationship between a 10s pulse current and a cutoff voltage provided by the embodiments of the present application; Figure 3 A schematic diagram of a linear relationship between a 30s pulse current and a cutoff voltage provided by the embodiments of the present application; Figure 4 A schematic diagram of a linear relationship between a 60s pulse current and a cutoff voltage provided by the embodiments of the present application. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present application will be described clearly and completely in combination with the drawings of the embodiments of the present application.

[0022] In the following description, the terms "first", "second" are only for the purpose of description, and cannot be understood as indicating or implying relative importance. The following description provides a plurality of embodiments of the present application, and different embodiments can be replaced or combined, so the present application can also be considered to include all possible combinations of the same and / or different embodiments described. Therefore, if one embodiment includes features A, B, C, and another embodiment includes features B, D, the present application should also be considered to include one or more embodiments of all other possible combinations of A, B, C, and D, although the embodiment may not be explicitly described in the following content.

[0023] The following description provides examples and does not limit the scope, applicability or examples set forth in the claims. Changes can be made to the functions and arrangements of the described elements without departing from the scope of the present application. Various processes or components can be appropriately omitted, replaced or added in each example. For example, the described methods can be executed in different order from the described order, and various steps can be added, omitted or combined. In addition, features described with respect to some examples can be combined into other examples.

[0024] Referring to Figure 1 , Figure 1 is a flowchart of a method for testing peak current of a power battery provided in an embodiment of the present application. In the embodiment of the present application, the method comprises: S1, determining an actual capacity of a battery to be tested.

[0025] In the present application, before the peak current test of the battery to be tested is performed, the actual capacity of the battery to be tested should be determined first, which can be determined based on the battery technical conditions.

[0026] Based on the actual situation, the discharge cutoff voltage U0 in the technical conditions of the lithium iron phosphate battery is preferably 2.5 V, and the charging cutoff voltage U1 is preferably 3.65 V, and the remaining material system battery can be set according to the actual specification.

[0027] In the embodiment of the present application, step S1 specifically comprises: S1-1. Discharge at a constant current of 1 / 3C~1C to a cutoff voltage U0 at room temperature, and the standing time t1; S1-2. Charge at a constant current of 1 / 3C~1C to a cutoff voltage U1 at room temperature, and then charge at a constant voltage until the charging current drops to 0.05C, and the standing time t1; S1-3. Repeat steps S1-1 to S1-2 N times, and when the range of the discharge capacity of the last n times is less than a preset value of the rated capacity, take the average of the last n experimental results as the actual capacity at room temperature; wherein the preset value is a first percentage, the first percentage < 3%; N and n are positive integers, and N > 5 and n ≥ 3; t1 can be 60 min; and the room temperature can be selected as 25℃±2.

[0028] In the present application, the standard charge and discharge is performed at room temperature, and the average is obtained by multiple measurements on the basis of meeting the range, so as to effectively determine the actual capacity of the battery to be tested.

[0029] In specific implementation, the first percentage can be 3%, N can be 5, and n can be 3, that is, the standard charge and discharge step is repeated 5 times, and when the range of the discharge capacity of the last 3 times is less than 3% of the rated capacity, the experiment can be ended in advance, and the average of the last 3 experimental results is taken as the actual capacity at room temperature 25℃±2.

[0030] S2, determining a test condition of the battery to be tested; The test conditions include variable conditions and parameter conditions. The variable conditions include a target electric quantity, a target pulse duration, and a target temperature. The parameter conditions include a cutoff voltage. The influence condition of the cutoff voltage includes the target temperature, and the target temperature is an ambient temperature. The target pulse duration includes a plurality of pulse duration nodes.

[0031] In the embodiments of the present application, the test conditions include adjustable variable conditions and fixed parameter conditions. The parameter conditions can include a cutoff voltage. The influence condition of the cutoff voltage is an ambient temperature. The cutoff voltage is a cutoff voltage of the battery to be tested at a target temperature. That is, when the target temperature of the test is determined, the cutoff voltage should be the cutoff voltage at the corresponding temperature. Generally, the cutoff voltage is a range value.

[0032] For example, when the target temperature is ≤0℃, the cutoff voltage is 2.0V-2.1V. When the target temperature is >0℃, the cutoff voltage is 2.5V-2.6V. The above data are examples and do not represent the actual situation. The actual measured value of the battery to be tested at different ambient temperatures is accurate.

[0033] In the present application, the variables of the test conditions include a target electric quantity, a target pulse duration, and a target temperature. The target electric quantity and the target temperature should be based on actual selection. Generally, those skilled in the art have relatively clear division experience. The target pulse duration includes a plurality of pulse duration nodes. The distribution of the pulse duration nodes can be selected based on actual conditions, or selected by the tester, or determined based on the actual experience of those skilled in the art.

[0034] For example, the target electric quantity is a percentage of the SOC value of the remaining current of the battery to be tested. The range value is clear, that is, 0% to 100%. Therefore, the target electric quantity should not exceed this range when it is determined.

[0035] For example, the target temperature is based on the ambient temperature. The range of the ambient temperature is generally -30℃ to 45℃. Therefore, the target temperature should not exceed this range or be significantly higher than this range when it is determined.

[0036] For example, the target pulse duration represents the duration of the pulse current. Generally, the current duration is intermittent in the discharge phase and continuous in the charging phase. Therefore, the pulse duration nodes can be selected autonomously when the target pulse duration is determined.

[0037] In one implementation manner, step S2 specifically includes: The target electric quantity is a percentage of the SOC value of the remaining electric quantity of the battery to be tested. The target electric quantity is divided into a plurality of percentages of the SOC value based on the actual capacity. When the test conditions are determined, one percentage of the SOC value is selected at will. The target temperature is divided into multiple gradient values based on the ambient temperature, and one of the gradient values is selected at will when determining the test condition; The target pulse duration includes multiple pulse duration nodes, and the maximum pulse duration node is determined first when determining the test condition, and other pulse duration nodes are selected in turn based on the maximum pulse duration node; The cut-off voltage is determined based on the gradient values of the target temperature, and the cut-off voltage of the battery to be tested at each gradient value is obtained, and the corresponding cut-off voltage is retrieved based on the selected target temperature when determining the test condition.

[0038] For example, the target electric quantity can be divided into six SOC value percentages, such as 5%, 10%, 30%, 50%, 70%, and 90%; the target temperature can have seven gradients, such as -30℃, -20℃, -10℃, 0℃, 10℃, 25℃, and 45℃; the target pulse duration can include three pulse duration nodes, such as 10s, 30s, and 60s; and the cut-off voltage is determined based on the gradient value of the selected target temperature.

[0039] S3, peak current test; In the test condition, the maximum value of the target pulse duration is used to perform peak current test based on the preset multiple reference current values, and multiple measured pulse currents are obtained, and the voltage value in the whole pulse process is recorded and sampled to obtain the measured cut-off voltage corresponding to each pulse duration node.

[0040] In the embodiments of the present application, the peak current test includes charging test and discharging test, and the discharging test is taken as an example for explanation.

[0041] Secondly, when performing the peak current test, the target pulse duration includes multiple pulse duration nodes, and multiple reference current values are preset. When taking an example for explanation, the number of current reference values is specified, and three reference current values are taken as an example for explanation. For example, a first reference current value, a second reference current value, and a third reference current value are preset. The number of pulse duration nodes included in the target pulse duration is specified, and three nodes are taken as an example for explanation. For example, the pulse duration includes a first pulse duration node, a second pulse duration node, and a third pulse duration node.

[0042] In one implementation manner, in the discharging test, step S3 specifically includes: S3-1. Discharge at 1 / 3C~1C constant current to the target electric quantity at room temperature; S3-2. Adjust the target temperature T of the test equipment oven, and stand for a time t2; S3-3. Discharge to the maximum value of the target pulse length with I1 constant current, obtain the measured pulse current of I1, record the pulse capacity Q1 of this step, sample and record the voltage value of the whole process of the pulse, and intercept the measured cut-off voltage V1, V2, V3 corresponding to three pulse length nodes; S3-4. After standing for time t2, depolarize, charge to Q1 with I4 constant current, and return to the target capacity; after returning the SOC, stand for time t2, and depolarize; S3-5. Discharge to the maximum value of the target pulse length with I2 constant current, obtain the measured pulse current of I2, record the pulse capacity Q2 of this step, sample and record the voltage value of the whole process of the pulse, and intercept the measured cut-off voltage V4, V5, V6 corresponding to three pulse length nodes; S3-6. After standing for time t2, depolarize, charge to Q2 with I4 constant current, and return to the target capacity; after returning the SOC, stand for time t2, and depolarize; S3-7. Discharge to the maximum value of the target pulse length with I3 constant current, obtain the measured pulse current of I3, record the pulse capacity Q3 of this step, sample and record the voltage value of the whole process of the pulse, and intercept the measured cut-off voltage V7, V8, V9 corresponding to three pulse length nodes; S3-8. After standing for time t2, depolarize, charge to Q3 with I4 constant current, and return to the target capacity; after returning the SOC, stand for time t2, and depolarize; Wherein, I1 is the first current reference value, I2 is the second current reference value, and I3 is the third current reference value; in step S3, when the target temperature is 25℃, t2=60min; when the target temperature is greater than 0℃, t2=120min; when the target temperature is less than or equal to 0℃, t2=720min; When the target temperature is less than or equal to 0℃, I4=0.05C; when the target temperature is greater than 0℃, I4=1 / 3C.

[0043] Wherein, the voltage sampling recording frequency / interval can be 0.1s, and the normal temperature can be 25℃±2.

[0044] In the embodiment of the application, when the SOC is returned, the pulse capacity (Q1, Q2, Q3) discharged with I4 constant current is charged, and the purpose is to return the SOC to the target capacity.

[0045] In the embodiment of the application, in the charging test, the pulse constant current (I1, I2, I3) in step S3 can be discharged to be changed to the pulse constant current (I1, I2, I3) charged, and the constant current (I4) in the return SOC can be changed to be discharged.

[0046] In a specific test case, the battery to be tested is an LFP power battery, and the rated capacity C = 166 Ah. The measured data obtained by peak current test under the test conditions of target temperature -20℃, target current 50% SOC, and pulse duration node 10s, 30s, and 60s are shown in Table 1 below:

[0047] wherein the unit of current is A and the unit of voltage is V.

[0048] S4, calculating the theoretical peak current; wherein the measured data obtained by peak current test under the same pulse duration node and different reference current values are output as a set of theoretical data, and the theoretical peak current under each pulse duration node is calculated based on the theoretical data of each pulse duration node; the measured data includes measured cutoff voltage and measured pulse current.

[0049] Based on the measured data obtained in step S3, the measured data obtained by peak current test under the same pulse duration node and different reference current values can be output as a set of theoretical data. For example, the theoretical data of one node includes three data points, each data point is composed of measured cutoff voltage and measured pulse current, and the relationship between the cutoff voltage and the pulse current is approximately linear.

[0050] Thus, in the coordinate system composed of measured pulse current and measured cutoff voltage, a curve can be fitted based on the three data points, and the theoretical peak current, i.e. the theoretical peak current, can be obtained through the curve.

[0051] In this way, the curves and the theoretical peak currents corresponding to multiple pulse duration nodes can be obtained in sequence.

[0052] In one feasible embodiment, in step S4, the theoretical peak current under each pulse duration node is calculated based on the theoretical data of each pulse duration node, which specifically includes: S4-1. Obtain the theoretical data of the first pulse duration node, which includes a first data point composed of measured pulse current and measured cutoff voltage obtained by peak current test at a first reference current value, a second data point composed of measured pulse current and measured cutoff voltage obtained by peak current test at a second reference current value, and a third data point composed of measured pulse current and measured cutoff voltage obtained by peak current test at a third reference current value; S4-2. Establish a first coordinate system with measured pulse current as the abscissa and measured cutoff voltage as the ordinate, and fit a first curve in the first coordinate system according to the theoretical data, wherein the first curve is a peak current function curve corresponding to the first pulse duration node of the battery to be tested under the test conditions. S4-3. Repeat steps S4-1 to S4-2 to obtain the peak current function curve corresponding to other pulse duration nodes of the battery to be tested under the test condition; S4-4. Calculate the theoretical peak current of each pulse duration node based on the peak current function curve corresponding to each pulse duration node.

[0053] For example, based on the data in Table 1, a first coordinate system is established, and a first curve is fitted in the first coordinate system, as shown in Figure 2 The abscissa of the intersection of the first curve and the abscissa axis is the theoretical peak current.

[0054] It can be understood that based on the theoretical data of the second pulse duration node, a second coordinate system can be constructed, and a second curve can be fitted in the second coordinate system, as shown in Figure 3 , and the theoretical peak current corresponding to the second pulse duration node is obtained. The third pulse duration node is the same, as shown in Figure 4 .

[0055] Based on Figure 2 , Figure 3 , Figure 4 , three relatively certain function relationships can be obtained in turn, and the theoretical peak current can be obtained by calculation in the corresponding coordinate system. The theoretical peak current under the test condition (below) can be calculated by linear interpolation method, and the approximate linear difference value is: I 理论1 The value of I 理论2 is 557, and the value of I 理论3 is 518.

[0056] Under the same test condition (only including target power and target temperature), the theoretical peak current is distinguished by the pulse duration node, and the theoretical peak current of each node can be obtained. By adjusting the interception time point, the theoretical peak current of any selected node within the maximum pulse duration range can be obtained based on the maximum pulse duration.

[0057] Based on the curve fitting method of step S4, at least three groups of reference current selection ranges can be preset, and the first reference current value, the second reference current value, and the third reference current value are determined before the peak current test. Specifically, the division of the selection range of the three groups of reference currents can be implemented based on the historical parameter abundance of the same type of battery, or based on the range of the rate, and the selection of the reference current value can fall within the interval more suitable for fitting the curve, so that the selection of the reference current value is not dependent on experience.

[0058] Taking three groups as an example, the selection range of the three reference currents is specifically a first reference range, a second reference range, and a third reference range, wherein the first reference current value is determined based on the first reference range, the second reference current value is determined based on the second reference range, and the third reference current value is determined based on the third reference range.

[0059] It should be clear that the first reference range, the second reference range, and the third reference range can pull apart the range of the multiple, so that the three data points in a set of theoretical data obtained by respectively performing peak current tests based on the three reference current values at the same pulse duration node are uniformly distributed on the peak current function curve.

[0060] For example, taking the first curve as an example, the overall span of the three data points on the first curve accounts for at least eighty percent of the overall length of the curve, and the overall length of the curve is calculated from the first data point on the left as the starting point to the intersection of the curve and the horizontal coordinate axis as the end point.

[0061] In specific implementation, the selection range of I1 can be 0.3C~0.7C, the selection range of I2 can be 1C~1.5C, and the selection range of I3 can be 2C~3.5C; secondly, the multiple interval can be appropriately pulled apart according to different temperatures and SOC values, so that the linear trend is better.

[0062] S5, pulse actual measurement verification of the theoretical peak current; Among them, the theoretical peak current under each pulse duration node is brought into the pulse actual measurement verification, and the pulse test is tested based on the theoretical peak current corresponding to each pulse duration node with each pulse duration node, the end voltage value is sampled and recorded, and if the end voltage value is within the cut-off voltage range corresponding to the corresponding pulse duration node, the theoretical peak current is effective.

[0063] In the embodiments of the present application, the pulse actual measurement verification includes charging actual measurement verification and discharging actual measurement verification, which is explained and described taking the discharging actual measurement verification as an example.

[0064] In one specific embodiment, during the discharging actual measurement verification, step S5 specifically includes: S5-1. I 理论1 Constant current discharge to the first pulse duration node, record the pulse capacity Q4 of this step discharge, and record the corresponding end voltage value V10; S5-2. Resting time t2, depolarization, and charging to Q4 with I4 constant current, and returning to the target capacity; after returning the SOC, resting time t2, and depolarization. S5-3. I 理论2 Constant current discharge to the second pulse duration node, record the pulse capacity Q5 of this step discharge, and record the corresponding end voltage value V11; S5-4. The standing time t2 after depolarization, the charge is filled to Q5 with I4 constant current, and the target charge is recalled; after recalling the SOC, the standing time t2, depolarization; S5-5. I 理论3 is discharged to the third pulse length node, and the terminal voltage value V12 is recorded.

[0065] In this application, when performing charging measurement verification, the pulse constant current (I 理论1 , I 理论2 , I 理论3 ) discharge in step S5 can be changed to pulse constant current (I 理论1 , I 理论2 , I 理论3 ) charging, and the constant current (I4) charging in the recall SOC is changed to constant current (I4) discharge.

[0066] It should be clear that I4 and t2 in step S5 should also follow the value conditions in step S3.

[0067] Based on the data in Table 1, I 理论1 is I 理论10s , the value is 572; I 理论2 is I 理论30s , the value is 557; I 理论3 is I 理论60s , the value is 518; the theoretical value measurement verification result is as follows Table 2:

[0068] According to the target temperature, the cut-off voltage, i.e. the target cut-off voltage in Table 2, can be obtained, and the effectiveness of the theoretical peak current can be judged based on the cut-off voltage.

[0069] In one specific embodiment, in step S5, the effectiveness of the theoretical peak current is judged, specifically including: Based on the target temperature, the corresponding cut-off voltage is obtained; When any one of the V10, V11, V12 data is obtained, it is judged whether it matches the cut-off voltage: If it matches, the theoretical peak current is effective; If it does not match, the theoretical peak current is invalid; Wherein, the cut-off voltage is a range parameter, when the terminal voltage value in step S5 is within the range of the cut-off voltage, it is matched; otherwise, it is not matched.

[0070] The theoretical peak current is effective, which can be considered as accurate.

[0071] Taking the target power divided into six SOCs (e.g., 5%, 10%, 30%, 50%, 70%, 90%), the target temperature with seven gradients (e.g., -30℃, -20℃, -10℃, 0℃, 10℃, 25℃, 45℃), and the target pulse duration including three pulse duration nodes (e.g., 10s, 30s, 60s) as an example, based on the peak current test method of this application, the overall test cycle is 1.5 days, while using the traditional test method, an SOC test at one temperature point requires 2-6 days. Obviously, the peak current test method of this application not only has a clear periodicity, but also has obvious period advantages.

[0072] The traditional test method steps can be specifically referred to as follows: Step 1: DC 10s Imax 1) Adjust the temperature to 25°C (room temperature) and let it stand for 300 minutes; 2) 1 / 3C CC to 3.65V; 3.65V CV to 0.05C 3) Stand for 30 minutes to depolarize; 4) Use 1 / 3C0 DC Xmin (adjust to n% SOC); 5) Adjust the temperature to Z °C and let it stand for H minutes (Z≤0, H=480 minutes; Z>0, H=300 minutes); 6) Record the discharge amount Q1 at Y DC for 10s (Z≤0, set the step cutoff voltage to 2.0V; Z>0, set the step cutoff voltage to 2.5V); where Y represents the current value selected this time; 7) Let stand for 30 minutes to depolarize; 8) Use k CC to Q1 to call back SOC (Z≤0, k=0.05C; Z>0, k=1 / 3C; set the step cutoff voltage = 3.65V); 9) Let stand for 60 minutes to depolarize; 10) Repeat steps 6) to 9) until the maximum discharge current value for 10 seconds is determined at the current temperature and SOC. Repeat steps 1) to 9) to complete the DC 10s Imax test for all temperatures and SOC. The temperature sequence is: 25°C / -30°C / -20°C / -10°C / 0°C / 10°C / 45°C. The SOC is tested from low to high, for example, 5%, 10%, 30%, 50%, 70%, and 90%. Judgment conditions: When Z≤0, the voltage at the end of 10s is 2.0±0.05V; when Z>0, the voltage at the end of 10s is 2.5±0.05V. When these conditions are met, the corresponding current value is recorded as Imax and recorded in Table 1, which is the effective peak current.

[0073] When the pulse length is adjusted, the effective peak current obtained at the current pulse length is not applicable to the adjusted pulse length, therefore, the above steps should be tested again with the adjusted pulse length, so as to obtain the effective peak current corresponding to the adjusted pulse length.

[0074] It should be noted that, for the foregoing method embodiments, in order to simply describe, they are all expressed as a series of action combinations, but those skilled in the art should know that the present application is not limited by the order of the described method steps, because according to the present application, certain steps can be performed in other order or simultaneously. Secondly, those skilled in the art should know that the embodiments described in the specification all belong to preferred embodiments, and the methods and limitations involved are not necessarily required by the present application.

[0075] In the above embodiments, the description of each embodiment has its own emphasis, and the parts not described in detail in a certain embodiment can be referred to the related description of other embodiments.

[0076] The above are only exemplary embodiments of the present disclosure, and cannot limit the scope of the present disclosure. That is, any equivalent changes and modifications made in accordance with the teachings of the present disclosure are still within the scope of the present disclosure. Those skilled in the art will easily think of embodiments of the present disclosure after considering the specification and practicing the disclosure herein. The present application is intended to cover any variations, uses or adaptive changes of the present disclosure, which follow the general principles of the present disclosure and include common knowledge or conventional technical means in the art not disclosed in the present disclosure. The specification and examples are only considered as exemplary, and the scope and spirit of the present disclosure are defined by the claims.

Claims

1. A method for testing peak current of a power battery, characterized in that: The method comprises: S1. Determine the actual capacity of the battery to be tested; S2. Determine the test conditions of the battery to be tested; The test conditions include variable conditions and parameter conditions, wherein the variable conditions include: target power, target pulse duration, and target temperature; the parameter conditions include a cutoff voltage, and the influencing condition of the cutoff voltage includes the target temperature, which is the ambient temperature; the target pulse duration includes multiple pulse duration nodes; S3, peak current test; Under the test conditions, peak current tests are performed based on multiple preset reference current values ​​and the maximum value of the target pulse duration to obtain multiple measured pulse currents, sample and record the voltage value of the entire pulse process, and intercept the measured cut-off voltage corresponding to each pulse duration node; S4. Calculate the theoretical peak current; The measured data obtained by performing peak current tests on the same pulse duration node at different reference current values ​​are output as a set of theoretical data, and the theoretical peak current at each pulse duration node is calculated based on the theoretical data of each pulse duration node; the measured data includes the measured cut-off voltage and the measured pulse current; S5. Pulse measurement verification of theoretical peak current; The theoretical peak current under each pulse duration node is brought into the pulse measurement verification. Based on the theoretical peak current corresponding to each pulse duration node, a pulse test is performed on each pulse duration node respectively, and the terminal voltage value is sampled and recorded. If the terminal voltage value is within the cut-off voltage range corresponding to the corresponding pulse duration node, the theoretical peak current is valid.

2. The method according to claim 1, characterized in that The influencing condition of the cut-off voltage is the ambient temperature of the battery to be tested, and the cut-off voltage is the cut-off voltage of the battery to be tested measured at the target temperature.

3. The method according to claim 1, characterized in that Step S1 specifically includes: S1-1. At room temperature, discharge at a constant current of 1 / 3C to 1C to a cutoff voltage of U0, and wait for t1. S1-2. Charge at room temperature at a constant current of 1 / 3C to 1C to the end voltage U1, then switch to constant voltage charging until the charging current drops to 0.05C. Stop charging and let stand for time t1. S1-3 steps S1-1 to S1-2 are repeated N times, when the range of the discharge capacity of n consecutive times is less than the preset value of the rated capacity, take the average value of the experimental results of n consecutive times as the actual capacity at room temperature; The preset value is a first percentage, which is less than 3%; N and n are both positive integers, and N is greater than 5 and n is greater than or equal to 3; and t1 is 60 minutes.

4. The method according to claim 1, wherein The peak current test includes a charging test and a discharging test, and the pulse measurement verification includes a charging measurement verification and a discharging measurement verification; the target pulse duration includes a first pulse duration node, a second pulse duration node, and a third pulse duration node, and a first reference current value, a second reference current value, and a third reference current value are preset.

5. The method according to claim 4, characterized in that During the discharge test, step S3 specifically includes: S3-1. At room temperature, discharge the battery at a constant current of 1 / 3C to 1C to the target charge. S3-2. The test equipment incubator is adjusted to the target temperature T and allowed to stand for a period of time t2; S3-3. I1 is discharged at a constant current to the maximum target pulse duration, and the measured pulse current of I1 is obtained. The pulse capacity Q1 of the discharge step is recorded at the same time. The voltage value of the whole pulse process is sampled and recorded, and the measured cut-off voltage V1, V2, and V3 corresponding to the three pulse duration nodes are intercepted; S3-4. After depolarization at rest for t2, charge Q1 with constant current I4 and return it to the target charge; after SOC is returned, rest for t2 and depolarize. S3-5. I2 constant current discharge to the maximum target pulse duration, obtain the measured pulse current I2, while recording the pulse capacity Q2 of the discharge step, sampling and recording the voltage value of the pulse throughout the process, and intercepting the three pulse duration nodes corresponding to the measured cut-off voltage V4, V5, V6; S3-6. After depolarization at rest for t2, charge Q2 with constant current I4 and return to the target charge; after SOC is returned to normal, rest for t2 and depolarize. S3-7. I3 constant current discharge to the maximum target pulse duration, obtain the measured pulse current I3, and record the pulse capacity Q3 of the discharge step, using the recorded pulse voltage value of the entire process, and intercept the three pulse duration nodes corresponding to the measured cut-off voltage V7, V8, V9; S3-8. After depolarization, stand for t2 and charge Q3 with constant current I4 until the target charge is reached. After SOC is reset, stand for t2 and depolarize. Wherein, I1 is the first current reference value, I2 is the second current reference value, and I3 is the third current reference value; when the target temperature is 25°C, t2 = 60 min; when the target temperature is greater than 0°C, t2 = 120 min; when the target temperature is less than or equal to 0°C, t2 = 720 min; When the target temperature is less than or equal to 0℃, I4=0.05C; when the target temperature is greater than 0℃, I4=1 / 3C.

6. The method according to claim 4, characterized in that During the discharge measurement verification, step S5 specifically includes: S5-1. Take I 理论1 Discharge at a constant current until the first pulse duration node is reached, while recording the pulse capacity Q4 of this step and the corresponding terminal voltage value V10; S5-2. After depolarization, the battery is charged to Q4 with a constant current of I4 and the battery is returned to the target capacity. After the SOC is returned, the battery is depolarized after a rest period of t2. S5-3. Take I 理论2 Discharge at a constant current until the second pulse duration node is reached, while recording the pulse capacity Q5 of this step and the corresponding terminal voltage V11; S5-4. After standing for t2, depolarization, charge Q5 with constant current I4 and call back to the target charge; after calling back SOC, stand for t2 and depolarize; S5-5. Take I 理论3 The constant current is discharged to the third pulse duration node, and the terminal voltage value V12 is recorded at the same time.

7. The method according to claim 6, characterized in that Step S5 further includes: Acquiring the corresponding cut-off voltage based on the target temperature; When any one of the data of V10, V11, and V12 is obtained, it is determined whether it matches the cut-off voltage: If they match, the theoretical peak current is valid; If they do not match, the theoretical peak current is invalid; The cut-off voltage is a range parameter. When the terminal voltage value in step S5 is within the range of the cut-off voltage, it is a match; otherwise, it is a mismatch.

8. The method according to claim 4, characterized in that In step S4, the theoretical peak current at each pulse duration node is calculated based on the theoretical data of each pulse duration node, specifically including S4-1. Obtain theoretical data of the first pulse duration node, the theoretical data including a first data point consisting of a measured pulse current and a measured cut-off voltage obtained by performing a peak current test with a first reference current value, a second data point consisting of a measured pulse current and a measured cut-off voltage obtained by performing a peak current test with a second reference current value, and a third data point consisting of a measured pulse current and a measured cut-off voltage obtained by performing a peak current test with a third reference current value; S4-2. A first coordinate system is established with the measured pulse current as the abscissa and the measured cut-off voltage as the ordinate. A first curve is fitted in the first coordinate system based on the theoretical data. The first curve is a peak current function curve corresponding to the first pulse duration node of the battery under test conditions. S4-3 repeat steps S4-1 to S4-2, to obtain the peak current function curve corresponding to other pulse duration nodes of the battery under test conditions; S4-4. Calculate the theoretical peak current of each pulse duration node based on the peak current function curve corresponding to each pulse duration node.

9. The method according to claim 7, characterized in that Preset at least three groups of reference current selection ranges, and determine a first reference current value, a second reference current value, and a third reference current value before performing a peak current test; The selection ranges of the three groups of reference currents are specifically a first reference range, a second reference range, and a third reference range. The first reference range, the second reference range, and the third reference range are separated by a magnification range so that three data points in a set of theoretical data obtained by performing peak current tests based on the three reference current values ​​for the same pulse duration node are evenly distributed on the peak current function curve. The first reference current value is determined based on the first reference range, the second reference current value is determined based on the second reference range, and the third reference current value is determined based on a third reference range.

10. The method according to claim 1, characterized in that Step S2 specifically includes: The target power is a percentage of the SOC value of the remaining power of the battery to be tested, the target power is divided into multiple SOC value percentages based on the actual capacity, and one SOC value percentage is arbitrarily selected when determining the test condition; The target temperature is divided into a plurality of gradient values ​​based on the ambient temperature, and one of the gradient values ​​is arbitrarily selected when determining the test condition; The target pulse duration includes multiple pulse duration nodes. When determining the test conditions, the maximum pulse duration node is determined first, and then other pulse duration nodes are selected in sequence based on the maximum pulse duration node. The cutoff voltage is measured based on each gradient value of the target temperature to obtain the cutoff voltage of the battery to be tested at each gradient value. When determining the test condition, the corresponding cutoff voltage is retrieved based on the selected target temperature.

Images