Sorting method for energy storage batteries

Abstract

The invention discloses an energy storage battery sorting method, which comprises the following steps: aiming at the internal resistance difference and voltage difference change of a battery cell, adopting a double-channel test method, testing the internal resistance of the battery cell by a main channel, testing the current and time by an auxiliary channel under the condition of monitoring voltage, calculating the capacity by using an ampere-hour integral method, and finally grading the capacity and matching. Finally, the consistency of voltage, internal resistance, capacity and charge-discharge curves of each battery cell in the module is realized, the cycle life is more than or equal to 10000 times, and the sorting result is more accurate; meanwhile, the two channels communicate independently, receive and send instructions, complete the test and then eliminate errors by superimposing an ampere-hour integral method, so that the test result is ensured to be independent, complete and accurate, and the internal consistency of the module is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy storage systems, and in particular to a method for sorting batteries for energy storage. Background Art

[0002] With the large-scale access to the power grid, the supply and demand sides of the power system show obvious random characteristics, which brings new challenges to the power grid's ability to accept new energy and its safe and stable operation. In order to solve the problem of time and space mismatch of renewable energy generation, it is necessary to introduce an efficient system with long-term energy storage capacity to ensure the smooth operation of the power grid.

[0003] Among many energy storage technologies, flow batteries have received widespread attention due to their long life cycle. However, the relatively low energy density and low system efficiency of flow batteries have limited their popularity in larger-scale applications. In contrast, lithium-ion battery energy storage technology has a more prominent position in the current market due to its relatively high energy density and system efficiency.

[0004] Ultra-large lithium-ion battery energy storage systems face the problem of inconsistent cell performance because they require the use of a large number of cells. The differences in voltage, internal resistance and capacity of these cells will lead to increased errors in the state of charge estimation, thus affecting the performance and reliability of the entire energy storage system. There is a bucket short board effect in the battery charging and discharging process, that is, the overall performance of the battery module is often limited by the worst cell. If there is inconsistency between the cells in the module, then during the charging and discharging process, the cell with the worst performance may be overcharged or over-discharged, which will not only reduce the efficiency of the entire system, but also cause irreversible damage to the battery. Therefore, this inconsistency will greatly shorten the cycle life of the battery module, and it is difficult to achieve a cycle life of more than 10,000 times. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a method for sorting batteries for energy storage.

[0006] In order to have a basic understanding of some aspects of the disclosed embodiments, a brief summary is given below. This summary is not intended to be a general review, nor is it intended to identify key / important components or to delineate the scope of protection of these embodiments. Its only purpose is to present some concepts in a simple form as a preface to the detailed description that follows.

[0007] The present invention adopts the following technical solution:

[0008] The present invention provides a method for sorting batteries for energy storage, including: battery pack testing and capacity sorting and grouping;

[0009] The battery pack is tested using dual channels, the dual channels including a main channel and an auxiliary channel, the main channel is used to measure the internal resistance of the battery cell, and the auxiliary channel is used to calibrate the capacity of the battery cell;

[0010] The battery pack test process includes multiple charge and discharge cycles, and the charge and discharge cycles include the following steps:

[0011] S1: Maintain constant temperature for 30 minutes;

[0012] S2: constant current discharge, and the discharge current is 0.125C, until the discharge cut-off condition is reached;

[0013] S3: Maintain constant temperature for 15 minutes;

[0014] S4: constant current and constant voltage charging, and the charging current is 0.125C, until the charging cut-off condition is reached;

[0015] S5: Maintain constant temperature for 15 minutes.

[0016] Furthermore, during the S2 constant current discharge process and the S4 constant current constant voltage charging process, the main channel measures the internal resistance of the battery cell and the change in resistance of the internal resistance of the battery cell with changes in current and voltage, and the auxiliary channel measures the capacity of the battery cell and the charging curve.

[0017] Furthermore, the main channel uses pulse current to measure the internal resistance of the battery cell, which specifically includes the following steps: discharging the battery cell to a specified voltage, discharging with a nominal constant current and then pausing for 15 seconds, and then charging with a constant current and constant voltage, and obtaining the charging internal resistance and the discharging internal resistance in turn, and solving the battery cell internal resistance using the mean method using the following formula:

[0018]

[0019] In the above formula, U t1 is the peak voltage of the pulse current; U t0 is the pulse current valley voltage; I pulse is the pulse current value.

[0020] Furthermore, the ampere-hour integration method is used to calculate the battery cell capacity, and the calculation formula is as follows:

[0021] S = S0-η∫I(t)dt / Q1;

[0022] In the above formula, S0 is the initial value of the battery cell's charge; η is the Coulomb efficiency; I(t) is the current at time t; Q1 is the rated capacity of the battery.

[0023] Furthermore, the battery pack testing process is carried out at 25°C±2°C.

[0024] Furthermore, the discharge cut-off condition refers to that the discharge cut-off voltage is 2.5V; and the charge cut-off condition refers to that the charge cut-off voltage is 3.65V.

[0025] Furthermore, the main channel and the auxiliary channel use the TP8485E chip to switch the electrical signal of the test data into an optical signal, and transmit it through the RS485 communication optical cable. At the same time, the CA-IS3722 dual-channel isolator is used to isolate the optical signal of the main channel from the optical signal of the auxiliary channel.

[0026] Furthermore, a resistance tester is arranged in the main channel; and a voltmeter and an ammeter are arranged in the auxiliary channel.

[0027] Furthermore, the process of capacity division and grouping includes: according to the results of the battery pack test, the battery cells are divided into different levels according to the capacity; the battery cells with a difference in internal resistance less than 0.05mΩ and a difference in battery capacity less than 0.3% are grouped together to form a battery module.

[0028] Beneficial effects brought by the present invention: In view of the difference in internal resistance of the battery cell and the change in voltage and pressure difference, the present invention adopts a dual-channel testing method, the main channel tests the internal resistance of the battery cell, the auxiliary channel tests the current and time while monitoring the voltage, and then uses the ampere-hour integration method to calculate the capacity, and finally divides the capacity into groups, and finally achieves the consistency of the voltage, internal resistance, capacity, and charge and discharge curves of each battery cell inside the module, and achieves a cycle life of ≥10,000 times, and the sorting results are more accurate. At the same time, the two channels communicate, receive and send instructions independently, complete the test, and then superimpose the ampere-hour integration method to eliminate errors, which further ensures that the test results are independent, complete and accurate, and ensures the consistency within the module. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0030] Figure 1 It is a schematic diagram of the charge and discharge cycle of the present invention. DETAILED DESCRIPTION

[0031] The embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. It should be clear that the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] The consistency of each battery cell in a battery module refers to the degree of consistency in performance of all battery cells in the same module, which is crucial to the overall performance and life of the battery module. Among them, the factors affecting the consistency of each battery cell in a battery module mainly include voltage, internal resistance and capacity.

[0033] The voltage is the initial voltage of the battery when it is assembled. The initial voltage of each cell should be as consistent as possible when the battery module is assembled. Voltage differences may indicate different aging, remaining capacity or health conditions of the cells. If the initial voltage differences of the cells are large, some cells may be overcharged or over-discharged during the charge and discharge process, thus affecting the performance and life of the entire module.

[0034] The internal resistance is the AC internal resistance when fully charged. It is an indicator to measure the internal impedance of the battery cell. The difference in internal resistance may cause uneven current distribution in some batteries during discharge, thus affecting the overall performance of the module.

[0035] Capacity is the discharge capacity. Capacity consistency means that in the same charge and discharge cycle, the amount of charge that can be discharged by all cells should be similar. Capacity differences may cause some cells in the module to be exhausted prematurely during the cycle, thereby shortening the service life of the entire module.

[0036] The battery parameters for improving cell consistency include voltage, resistance, capacity, SOC, etc. SOC is the percentage of the remaining capacity of the cell, and the consistency of SOC is crucial for the accurate control of the battery management system. If the SOC of the cells is inconsistent, the battery management system may not be able to effectively balance the cells in the module, causing some cells to be overcharged or over-discharged. Through SOC estimation and balancing strategies, it is possible to ensure that the cells maintain a consistent SOC during the charging and discharging process, thereby improving the performance and safety of the entire module.

[0037] like Figure 1 As shown, in some illustrative embodiments, the present invention provides a method for sorting batteries for energy storage, including: battery pack testing and capacity sorting.

[0038] Battery pack testing refers to measuring key parameters of battery cells, such as voltage, internal resistance, and capacity. Capacity grouping refers to classifying the battery cells into different levels according to their capacity and grouping similar battery cells together based on the results of the battery pack test to reduce the performance differences between the battery cells. By testing capacity grouping, the performance consistency of each group of battery cells is ensured, thereby improving the overall performance and reliability of the battery pack, and reducing overcharging or over-discharging caused by differences in battery cell performance, thereby extending the battery life.

[0039] The present invention adopts dual channels to test the battery pack, and the dual channels include a main channel and an auxiliary channel. The main channel is used to measure the internal resistance of the battery cell, and the auxiliary channel is used to calibrate the capacity of the battery cell.

[0040] The battery pack test is completed during the charging and discharging process of the battery cell. The main channel and auxiliary channel are tested separately, and the battery pack test process is carried out at 25℃±2℃. This temperature range is set according to the optimal operating temperature range of the battery to ensure the stability of battery performance.

[0041] The battery pack test process includes multiple charge and discharge cycles, which include the following steps:

[0042] S1: Maintain constant temperature for 30 minutes.

[0043] Specifically, it means maintaining the temperature of the test environment of the battery cell at 25℃±2℃ for 30 minutes, which helps to evenly distribute the temperature inside the battery pack, that is, ensure that the battery pack is in a stable temperature state before the test begins to eliminate the impact of temperature fluctuations on the test results.

[0044] S2: Maintain constant current discharge until the discharge cut-off condition is reached.

[0045] The discharge process of the battery in actual use is simulated by constant current discharge, and the performance of the battery during the discharge process is tested. The discharge current is 0.125C, and 0.125C means that the battery is discharged at 0.125 times the rated capacity.

[0046] The discharge cut-off condition means that the discharge cut-off voltage is 2.5V. The discharge cut-off voltage is set to 2.5V so that when the voltage of any cell in the battery pack drops to 2.5V, the discharge process should stop immediately. This voltage threshold is to prevent the battery from over-discharging and avoid damage to battery performance and life.

[0047] During the discharge process, the voltage and current of the battery pack need to be monitored in real time to ensure that the discharge current remains constant. At the same time, since the performance of each battery cell in the battery pack may be different, there may be an imbalance between the batteries during the discharge process, which needs to be monitored and balanced by the battery management system.

[0048] During constant current discharge, the main channel measures the internal resistance of the battery cell and the change in resistance of the battery cell with changes in current and voltage. The auxiliary channel measures the battery cell capacity and charging curve for subsequent analysis.

[0049] S3: Maintain constant temperature for 15 minutes. Specifically, the temperature of the test environment of the battery cell is maintained at 25℃±2℃ for 15 minutes. The purpose of this step is to ensure that the battery is in a stable temperature environment during the test, thereby ensuring the accuracy and repeatability of the test results.

[0050] S4: Constant current and constant voltage charging until the charging cut-off condition is reached.

[0051] The battery is charged in constant current and constant voltage charging mode to reach a fully charged state, and the battery performance during the charging process is tested. During the charging process, the battery voltage, current and temperature need to be monitored in real time to ensure that the charging process is safe and reliable.

[0052] The charging current is 0.125C, which means the battery is charged at 0.125 times the rated capacity. The charging cutoff condition means that the charging cutoff voltage is 3.65V. When the battery voltage reaches 3.65V, charging should be stopped immediately to avoid overcharging. During the constant current and constant voltage charging process, the main channel measures the internal resistance of the battery cell and the change of the resistance value of the battery cell with the change of current and voltage, and the auxiliary channel measures the battery cell capacity and charging curve for subsequent analysis.

[0053] S5: Maintain constant temperature for 15 minutes.

[0054] S1-S5 completes one charge and discharge cycle. The number of cycles is determined based on experimental conditions and customer requirements, and generally 5-20 cycles are required.

[0055] In the present invention, according to the number of cycles of the battery pack test, in order to better count the battery characteristics, the main channel uses a pulse current to measure the internal resistance of the battery cell, which specifically includes the following steps:

[0056] The battery cell is discharged to a specified voltage, discharged with a nominal constant current, and then paused for 15 seconds, and then charged with a constant current and constant voltage, and the charging internal resistance and the discharging internal resistance are obtained in turn. The battery cell internal resistance is solved by the following formula using the mean method (solving the mean value of the battery cell internal resistance obtained in each cycle):

[0057]

[0058] In the above formula, U t1 is the peak voltage of the pulse current; U t0 is the pulse current valley voltage; I pulse is the pulse current value.

[0059] In the present invention, the ampere-hour integration method is used to calculate the cell capacity, and the calculation formula is as follows:

[0060] S = S0-η∫I(t)dt / Q1;

[0061] In the above formula, S0 is the initial value of the battery cell's charge; η is the Coulomb efficiency; I(t) is the current at time t; Q1 is the rated capacity of the battery.

[0062] The ampere-hour integration method is to calculate the amount of charge consumed during a period of time by integrating the current over time. After each test cycle is completed, the battery capacity may not be fully discharged, fully charged, or overcharged. As the number of test cycles increases, it will cause a larger test error. Therefore, the power value estimated by the ampere-hour integration method is more accurate. In addition, the ampere-hour integration method is relatively simple and has a small error. In actual application, the current and temperature in the ampere-hour integration method are usually feedback-corrected, and then estimated in combination with the open circuit voltage method, thereby improving the estimation accuracy.

[0063] In the process of estimating the cell capacity using the ampere-hour integration method, the initial value of the power is set, and when all single cells reach full power, the cell is judged to be in a full power state, that is, 100%. The cumulative power used during the discharge process is subtracted, and the cumulative power input during the charging process is added. The ratio to the rated capacity is the remaining power of the battery. The cumulative power belongs to the difference between a small part of the charging or discharging process during the test cycle, the difference between the charging and the full charge, or the overcharge margin, that is, the accumulation of each error. The error value is the difference between the comparison of each test current value and the standard value, and the cumulative amount of multiple tests.

[0064] Since the error power caused by multiple cycle tests will be accumulated in the discharge process, the accumulated power must be subtracted during the discharge process. Therefore, subtracting the accumulated power used during the discharge process will make the result more accurate, which is equivalent to the middle value of the regression normal distribution. At the same time, during the charging process, the error power caused by several cycle tests will be accumulated in the charging process power. Therefore, the input accumulated power must be added during the charging process to ensure the accuracy of the result. In addition, the battery will decay during use. If the initial capacity and resistance of the battery are consistent at the beginning, but after half a year or a year of use, the battery capacity remains 90% and 80%, then it will work at the lowest 80%. Therefore, the test requires the remaining power to be consistent, that is, the remaining power is 85% ± 1%, which is the best.

[0065] To ensure the accuracy of the state estimation, the current battery remaining power will be determined to be 100% when the next balancing is completed, and the battery remaining power will be determined to be 0% when the battery pack is fully used next time, eliminating the cumulative error of the ampere-hour integration method and ensuring more accurate testing.

[0066] The main channel and the auxiliary channel use the TP8485E chip to switch the electrical signal of the test data into an optical signal, and transmit it through the RS485 communication optical cable. At the same time, the CA-IS3722 dual-channel isolator is used to isolate the optical signal of the main channel from the optical signal of the auxiliary channel. The main and auxiliary channels are isolated from the battery management system circuit by the CA-IS3722 dual-channel isolator, and communicate with the external test circuit respectively. The isolated signal is converted into an RS485 communication signal. Since RS485 has the differential and half-duplex communication characteristics, the TP8485E chip transceiver function needs to be switched to convert the electrical signal into an optical signal. The optical coupler is designed to realize the transceiver mode switching function and the external signal detection function. The two channels are completed independently without interfering with each other, which improves the test accuracy.

[0067] A resistance tester is set in the main channel; a voltmeter and an ammeter are set in the auxiliary channel. The voltmeter monitors the cell voltage, monitors the start voltage and the cut-off voltage, and starts charging and discharging at the start voltage and stops charging and discharging at the cut-off voltage. The ammeter monitors the cell current, and the test current is to calculate the cell capacity based on the input current data and time.

[0068] In the present invention, the process of capacity division and grouping includes: according to the results of the battery pack test, the battery cells are divided into different levels according to the capacity; the battery cells with a difference in internal resistance of less than 0.05mΩ and a difference in battery capacity of less than 0.3% are grouped together to form a battery module. In order to limit the loss of battery pack capacity and life caused by differences in cell capacity and internal resistance, all battery cells are pre-evaluated through a dual-channel test method of capacity and internal resistance, and the battery cells with relatively concentrated parameters are placed in the optimized series path.

[0069] In view of the difference in the internal resistance of the battery cells and the change in the voltage differential, the present invention adopts a dual-channel testing method. The main channel tests the internal resistance of the battery cells, and the auxiliary channel tests the current and time while monitoring the voltage. The capacity is calculated by the ampere-hour integration method, and finally the capacity is divided into groups, so as to finally achieve the consistency of the voltage, internal resistance, capacity, and charge-discharge curve of each battery cell in the module, and achieve a cycle life of ≥10,000 times, and the sorting results are more accurate. At the same time, the two channels communicate, receive and send instructions independently, complete the test, and then superimpose the ampere-hour integration method to eliminate errors, which further ensures that the test results are independent, complete and accurate, and ensures the internal consistency of the module.

[0070] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A method for sorting batteries for energy storage, characterized in that: include: Battery pack testing and capacity distribution; The battery pack is tested using dual channels, the dual channels including a main channel and an auxiliary channel, the main channel is used to measure the internal resistance of the battery cell, and the auxiliary channel is used to calibrate the capacity of the battery cell; The battery pack test process includes multiple charge and discharge cycles, and the charge and discharge cycles include the following steps: S1: Maintain constant temperature for 30 minutes; S2: constant current discharge, and the discharge current is 0.125C, until the discharge cut-off condition is reached; S3: Maintain constant temperature for 15 minutes; S4: constant current and constant voltage charging, and the charging current is 0.125C, until the charging cut-off condition is reached; S5: Maintain constant temperature for 15 minutes.

2. A method for sorting energy storage batteries according to claim 1, characterized in that: During the S2 constant current discharge process and the S4 constant current constant voltage charging process, the main channel measures the internal resistance of the battery cell and the change in resistance of the battery cell with changes in current and voltage, and the auxiliary channel measures the capacity of the battery cell and the charging curve.

3. A method for sorting energy storage batteries according to claim 2, characterized in that: The main channel uses pulse current to measure the internal resistance of the battery cell, which specifically includes the following steps: The battery cell is discharged to a specified voltage, discharged with a nominal constant current, and then paused for 15 seconds, and then charged with a constant current and constant voltage, and the charging internal resistance and the discharging internal resistance are obtained in turn. The battery cell internal resistance is solved by the mean value method using the following formula: In the above formula, U t1 is the peak voltage of the pulse current; U t0 is the pulse current valley voltage; I pulse is the pulse current value.

4. A method for sorting energy storage batteries according to claim 3, characterized in that: The battery capacity is calculated using the ampere-hour integration method. The calculation formula is as follows: S = S0-η∫I(t)dt / Q1; In the above formula, S0 is the initial value of the battery cell's charge; η is the Coulomb efficiency; I(t) is the current at time t; Q1 is the rated capacity of the battery.

5. A method for sorting energy storage batteries according to claim 4, characterized in that: The battery pack test process is carried out at 25°C±2°C.

6. A method for sorting batteries for energy storage according to claim 5, characterized in that: The discharge cut-off condition refers to that the discharge cut-off voltage is 2.5V; the charge cut-off condition refers to that the charge cut-off voltage is 3.65V.

7. A method for sorting energy storage batteries according to claim 6, characterized in that: The main channel and the auxiliary channel use the TP8485E chip to switch the electrical signal of the test data into an optical signal, and transmit it through the RS485 communication optical cable. At the same time, the CA-IS3722 dual-channel isolator is used to isolate the optical signal of the main channel from the optical signal of the auxiliary channel.

8. A method for sorting energy storage batteries according to claim 7, characterized in that: A resistance tester is arranged in the main channel; a voltmeter and an ammeter are arranged in the auxiliary channel.

9. A method for sorting batteries for energy storage according to claim 8, characterized in that: The process of capacity division and grouping includes: according to the test results of the battery pack, the battery cells are divided into different levels according to capacity; the battery cells with a difference in internal resistance less than 0.05mΩ and a difference in battery capacity less than 0.3% are grouped together to form a battery module.

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