Capacity grading and matching method for echelon utilization of lithium iron phosphate cells

Abstract

The invention discloses a capacity grading and matching method for echelon utilization of lithium iron phosphate battery cells, and relates to the field of echelon utilization of battery cells, and the method comprises the following steps: testing electrical parameters of the battery cells in a working process to obtain a test result of the battery cells, and screening echelon battery cells according to the test result, and when various parameters among the echelon battery cells meet a preset standard, matching the echelon battery cells. In the prior art, the consistency of the polarization factor of the residual capacity on the cell dynamic curve state is not considered, the voltage consistency effect of the whole recombined echelon cell module is poor in the charging and discharging process, and the direct current internal resistance test needs to be independent of the residual capacity test, so that misjudgment exists. The internal polarization internal resistance of the battery cell is measured through the platform capacity ratio and the voltage rising method, so that direct-current internal resistance test items are reduced, and the voltage consistency of the echelon battery cell module is improved through the consistency matching of charging and discharging curve multi-platform capacity.

Description

Technical Field

[0001] The present application relates to the technical field of recycled battery cells, and in particular to a method for dividing and grouping recycled lithium iron phosphate battery cells. Background Art

[0002] Retired power batteries have great utilization value, but retired power batteries have complex retirement reasons (negative electrode structure damage and powder loss, electrode lack of liquid and drying up), and there are certain safety risks. In addition, retired power battery packs have some low health indexes. Therefore, before the retired cells are reused, the health of the retired cells must be evaluated, and the cells must be re-assembled to provide consistency for the retired batteries. Currently, the capacity division and grouping of retired cells still use the capacity division method of new cells, mainly evaluating their remaining capacity, AC internal resistance ACR, self-discharge K value, DC internal resistance DCR, and cell thickness.

[0003] However, its DC internal resistance value is affected by many factors such as temperature, battery cell SOC status, test current size, battery cell storage time, etc., and the DC internal resistance test needs to be independent of the remaining capacity test, so it is easy to have misjudgment. As for the remaining capacity, it currently mainly considers its single capacity division current and single discharge cut-off voltage capacity, without considering the consistency of its polarization factor on the dynamic curve state of its battery cell. The reorganized cascade battery module as a whole has the problem of poor voltage consistency during the charging and discharging process. Summary of the invention

[0004] The main purpose of the present application is to provide a method for dividing and grouping lithium iron phosphate batteries for cascade utilization, aiming to solve the technical problems that the voltage consistency of the reorganized cascade battery module as a whole is poor during the charging and discharging process and the DC internal resistance test needs to be independent of the remaining capacity test, which may lead to misjudgment.

[0005] To achieve the above-mentioned purpose, the present application proposes a method for dividing and grouping lithium iron phosphate batteries for cascade utilization, and the method for dividing and grouping lithium iron phosphate batteries for cascade utilization includes:

[0006] Testing the electrical parameters of the battery cell during operation to obtain the test results of the battery cell;

[0007] According to the test results, the battery cells are screened;

[0008] When various parameters between battery cells of different levels meet the preset standards, the battery cells of different levels are grouped.

[0009] Optionally, the electrical parameters include: residual capacity, constant current ratio, recovery voltage, platform capacity ratio, platform capacity ratio weight, self-discharge K value, AC impedance and open circuit voltage;

[0010] The step of testing the electrical parameters of the battery cell during operation to obtain the test result of the battery cell specifically includes:

[0011] Performing a capacity test on the battery cell to determine the residual capacity, constant current ratio, recovery voltage, platform capacity ratio and platform capacity ratio weight of the battery cell;

[0012] Performing an aging test on the battery cell to determine the self-discharge K value of the battery cell;

[0013] Perform internal resistance and open circuit voltage tests on the battery cell to determine the AC impedance and open circuit voltage of the battery cell.

[0014] Optionally, the step of performing a capacity test on the battery cell to determine the residual capacity, constant current ratio, recovery voltage, platform capacity ratio and platform capacity ratio weight of the battery cell specifically includes:

[0015] charging the battery cell to a first voltage using a first current and determining a charge capacity of the battery cell;

[0016] discharging the battery cell by a first current to a second voltage, and determining a discharge capacity of the battery cell;

[0017] The residual capacity, constant current ratio, recovery voltage, platform capacity ratio and platform capacity ratio weight of the battery cell are determined according to the first voltage, the second voltage, the charging capacity and the discharging capacity.

[0018] Optionally, the step of charging the battery cell by the first current until a first voltage is reached and determining the charging capacity of the battery cell specifically includes:

[0019] Performing constant current charging on the battery cell by a first current until a first termination voltage is reached, and determining a first charging capacity of the battery cell;

[0020] Performing constant current charging on the battery cell by using a first current until a second termination voltage is reached, and determining a second charging capacity of the battery cell;

[0021] The battery cell is charged at a constant voltage by a first current until a second termination voltage and a second termination current are reached, and a third charging capacity of the battery cell is determined.

[0022] Optionally, the step of discharging the battery cell by the first current until the second voltage is reached and determining the discharge capacity of the battery cell specifically includes:

[0023] Discharging the battery cell at a constant current by a first current until a third termination voltage is reached, and determining a fourth discharge capacity of the battery cell;

[0024] Discharging the battery cell at a constant current by a first current until a fourth termination voltage is reached, and determining a fifth discharge capacity of the battery cell;

[0025] The battery cell is discharged at a constant current by using a first current until a fifth termination voltage, and a sixth discharge capacity of the battery cell is determined.

[0026] Optionally, before the step of charging the battery cell by the first current until the first voltage is reached and determining the charging capacity of the battery cell, the method further includes:

[0027] Discharging the battery cell by a first current until a preset first voltage is reached;

[0028] The battery cell is discharged from the preset first voltage to a preset second voltage through a second current.

[0029] Optionally, after the step of discharging the battery cell by the first current until the second voltage is reached and determining the discharge capacity of the battery cell, the method further includes:

[0030] After the battery cell is left idle for a preset first time, a sixth termination voltage of the last preset second time is collected;

[0031] discharging the battery cell by a second current until a seventh termination voltage, and determining a seventh discharge capacity of the battery cell;

[0032] The battery cell is charged by the first current until a preset third voltage is reached, and an eighth cutoff capacity of the battery cell is determined.

[0033] Optionally, the step of performing an aging test on the battery cell to determine the self-discharge K value of the battery cell specifically includes:

[0034] Performing an aging test when the capacity of the battery cell is an eighth cutoff capacity;

[0035] Determine the test conditions of the aging test according to the aging test requirements;

[0036] Performing an aging test on the battery cell according to the test conditions, and determining the voltage of the battery cell before and after the aging test;

[0037] The self-discharge K value of the battery cell is determined according to the voltage before and after the battery cell aging test and the aging test temperature.

[0038] Optionally, the step of determining the residual capacity, constant current ratio, recovery voltage, platform capacity ratio and platform capacity ratio weight of the battery cell according to the first voltage, the second voltage, the charging capacity and the discharging capacity specifically includes:

[0039] determining a residual capacity of the battery cell according to the fourth discharge capacity, the fifth discharge capacity, the sixth discharge capacity, and the seventh discharge capacity;

[0040] Determining a constant current ratio of the battery cell according to the first charging capacity, the second charging capacity and the third charging capacity;

[0041] Determining a recovery voltage of the battery cell according to the fifth termination voltage and the sixth termination voltage;

[0042] According to the charging capacity and the discharging capacity, the platform capacity ratio and the platform capacity ratio weight are determined.

[0043] Optionally, when various parameters between battery cells of different orders meet preset standards, the step of grouping battery cells of different orders specifically includes:

[0044] When the residual capacity, constant current ratio, self-discharge K value, AC impedance, open circuit voltage difference and platform capacity ratio weight of each tier of battery cells meet the preset standards, the battery cells of each tier are grouped.

[0045] One or more technical solutions proposed in this application have at least the following effects:

[0046] The present application proposes a capacity division and grouping method for cascade utilization of lithium iron phosphate batteries, the capacity division and grouping method for cascade utilization of lithium iron phosphate batteries includes: testing the electrical parameters of the battery cells during operation to obtain the test results of the battery cells, screening the cascade batteries according to the test results, and grouping the cascade batteries when the parameters between the cascade batteries meet the preset standards. Compared with the current cascade batteries, which still borrow the capacity division method of new batteries in terms of capacity division and grouping, the remaining capacity is currently mainly considered for its single capacity division current and the capacity of a single discharge cut-off voltage, but the consistency of its polarization factor with the dynamic curve state of the battery cell is not considered. The reorganized cascade battery module as a whole has poor voltage consistency effect during the charging and discharging process and the DC internal resistance test needs to be independent of the remaining capacity test, which has misjudgment problems. In the process of battery cell capacity division, the internal polarization resistance of the battery cell is measured by the platform capacity ratio and the recovery voltage method, thereby reducing the DC internal resistance test items, and the voltage consistency of the cascade battery module is improved by the consistency grouping of the multi-platform capacity of the charge and discharge curve. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the embodiments of the present application 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, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0048] Figure 1It is a schematic diagram of the first process of the first embodiment of the method for dividing and grouping lithium iron phosphate batteries for cascade utilization proposed in the embodiment of the present application;

[0049] Figure 2 It is a schematic diagram of the first process of the second embodiment of the method for dividing and grouping lithium iron phosphate batteries for cascade utilization proposed in the embodiment of the present application;

[0050] Figure 3 It is a schematic diagram of the first process of the third embodiment of the method for dividing and grouping lithium iron phosphate batteries for cascade utilization proposed in the embodiment of the present application;

[0051] Figure 4 It is a schematic diagram of the first process of the fourth embodiment of the method for dividing and grouping lithium iron phosphate batteries for cascade utilization proposed in the embodiment of the present application;

[0052] Figure 5 It is a second flow chart of a fourth embodiment of the method for dividing and grouping lithium iron phosphate batteries for cascade utilization proposed in an embodiment of the present application;

[0053] Figure 6 A third flow chart of a fourth embodiment of the method for dividing and grouping lithium iron phosphate batteries for cascade utilization proposed in an embodiment of the present application;

[0054] Figure 7 A fourth flow chart of a fourth embodiment of the method for dividing and grouping lithium iron phosphate cells for cascade utilization proposed in an embodiment of the present application;

[0055] Figure 8 A second flow chart of a second embodiment of the method for dividing and grouping lithium iron phosphate cells for cascade utilization proposed in an embodiment of the present application;

[0056] Fig. 9 It is a second flow chart of the third embodiment of the method for dividing and grouping lithium iron phosphate batteries for cascade utilization proposed in the embodiment of the present application;

[0057] Fig.10 It is a schematic diagram of the second process of the first embodiment of the method for dividing and grouping lithium iron phosphate batteries for cascade utilization proposed in the embodiment of the present application;

[0058] Fig.11 This is a flow chart of the tiered battery cell capacity test in this application.

[0059] The purpose, features and advantages of this application will be further described in conjunction with the embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0060] It should be understood that the specific embodiments described herein are only used to explain the technical solutions of the present application and are not used to limit the present application.

[0061] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0062] It should be noted that all directional indications in the embodiments of the present application (such as up, down, left, right, front, back, etc.) are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0063] In addition, the descriptions of "first", "second", etc. in this application are only for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in this field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by this application.

[0064] The main solution of the embodiment of the present application is: by using the consistency of the capacity at the characteristic voltage point of the dynamic charge and discharge curve, the consistency of the battery pack during cascade utilization is improved, and the cascade battery cells are screened by testing and grouped according to preset standards, thereby extending the battery cell service life and reducing the cost of the energy storage system.

[0065] With the crisis of petrochemical energy, the rapid development and application of electric vehicles, the scale of electric vehicle power batteries is also expanding. Many power batteries have different degrees of battery aging and performance differences due to differences in battery production process control capabilities, battery pack grouping methods, and electric vehicle operating conditions (temperature and power), which cannot meet the power performance, cruising range and operating safety factors of electric vehicles. When the power battery capacity decays to 80% of the rated capacity, the power battery needs to be retired and replaced. However, through the cycle life test of retired lithium iron phosphate cells, it is not difficult to find that lithium iron phosphate cells still have excellent cycle performance when the capacity retention rate is 80%-50%. Its electrochemical performance far exceeds that of lead-acid batteries, and it has great recycling value. It can be used for application scenarios with low volume energy requirements or low power, such as low-speed vehicles, photovoltaic energy storage and communication backup power supply markets.

[0066] Although retired power batteries have great utilization value, they are retired for complex reasons (negative electrode structure damage and powder loss, electrode lack of liquid and drying up), and there are certain safety risks. In addition, retired power battery packs have some low health indexes. Therefore, before the retired cells are reused, the health of the retired cells must be evaluated, and the cells must be reassembled to provide consistency. Currently, the capacity division and grouping of retired cells still use the capacity division method of new cells, mainly evaluating their remaining capacity, AC internal resistance ACR, self-discharge K value, DC internal resistance DCR, and cell thickness.

[0067] However, its DC internal resistance value is affected by many factors such as temperature, battery cell SOC status, test current size, battery cell storage time, etc., and the DC internal resistance test needs to be independent of the remaining capacity test, so it is easy to have misjudgment. Secondly, for the remaining capacity, it currently mainly considers its single capacity division current and single discharge cut-off voltage capacity, without considering the consistency of its polarization factor on the dynamic curve state of its battery cell. The reorganized tiered battery module as a whole has the problem of poor voltage consistency during the charging and discharging process.

[0068] The present application provides a solution, and proposes a method for capacity division and grouping of lithium iron phosphate battery cells for cascade utilization. The method for capacity division and grouping of lithium iron phosphate battery cells for cascade utilization includes: testing the electrical parameters of the battery cells during operation to obtain the test results of the battery cells, screening cascade battery cells according to the test results, and grouping the battery cells of each cascade when the various parameters between the battery cells of each cascade meet the preset standards. Compared with the current tiered battery cells, which still use the new battery cell capacity division method in terms of capacity division and grouping, the remaining capacity is mainly considered at present, with the capacity of a single division current and a single discharge cut-off voltage, but the consistency of the polarization factor with the dynamic curve state of the battery cell is not considered. The reorganized tiered battery cell module as a whole has poor voltage consistency during the charging and discharging process, and the DC internal resistance test needs to be independent of the remaining capacity test, which may cause misjudgment. In the process of battery cell division, the platform capacity ratio and the recovery voltage method are used to measure the internal polarization resistance of the battery cell, thereby reducing the DC internal resistance test items, and the voltage consistency of the tiered battery cell module is improved through the consistency grouping of the multi-platform capacity of the charging and discharging curve.

[0069] Based on this, an embodiment of the present application provides a method for dividing and grouping lithium iron phosphate batteries for cascade utilization.

[0070] refer to Figure 1 , Figure 1 This is a flow chart of the first embodiment of the method for dividing and grouping lithium iron phosphate batteries for cascade utilization proposed in the embodiment of the present application.

[0071] Considering that the reorganized tiered battery module has poor voltage consistency during the charging and discharging process, in order to group the tiered batteries, Figure 1 As shown, the method for dividing and grouping lithium iron phosphate batteries for cascade utilization in this embodiment includes steps S10 to S30:

[0072] Step S10: testing the electrical parameters of the battery cell during operation to obtain the test results of the battery cell.

[0073] Step S20: Screening the inferior battery cells according to the test results.

[0074] Step S30: When various parameters between battery cells of different orders meet preset standards, the battery cells of different orders are grouped.

[0075] It should be noted that the battery cell refers to a retired power battery. The battery cell of the power battery is a lithium iron phosphate battery cell. The test results and electrical parameters of the battery cell include: residual capacity, constant current ratio, recovery voltage, platform capacity ratio, platform capacity ratio weight, self-discharge K value, AC impedance and open circuit voltage. Residual capacity is the remaining capacity, which refers to the amount of electricity that the battery can still store after a period of discharge. The residual capacity can be used to judge the life or health status of the battery. The constant current ratio refers to the ratio of the actual output current of the battery to the nominal current during the discharge process of the battery (especially the battery used in cascade). The constant current ratio of the battery cell is used to measure the current stability during the discharge process of the battery, which is of great significance for evaluating the performance and life of the cascade battery cell. The rebound voltage can be used as a reference indicator for evaluating the performance of cascade batteries. By measuring the rebound voltage after the discharge, the internal resistance and ion concentration recovery of the battery can be indirectly understood, thereby judging the health status and remaining capacity of the battery. Although the rebound voltage itself will not have a direct impact on the safety of the battery, an excessively high rebound voltage may mean that there are abnormalities inside the battery, such as excessive internal resistance or uneven distribution of ion concentration. These abnormalities may increase the safety risk of the battery in subsequent use. The platform capacity ratio usually refers to the ratio of the capacity released by the battery at a specific discharge stage (such as the characteristic voltage point of the dynamic charge and discharge curve) to the total capacity of the battery. The platform capacity ratio can be used to evaluate the performance of the battery in the cascade utilization process, as well as the overall consistency and stability of the battery pack. The self-discharge K value is an important indicator to measure the degree of voltage reduction of the battery cell within a specific time interval.

[0076] It can be understood that second-hand batteries refer to batteries that have been used for a period of time in electric vehicles, energy storage systems or other fields. Although the performance of these batteries may not be as strong as new batteries, they still retain a certain capacity and performance. Through a series of testing, screening and reorganization processes, these batteries can continue to function in scenarios where performance requirements are not so high, thereby achieving secondary utilization of resources.

[0077] It should be noted that the preset standards include the technical requirements and weight levels of tiered battery cell grouping. The various parameters and preset standards between each tier of battery cells include: AC impedance difference (technical requirements need to be ≤1%, weight level is 1), self-discharge K value difference (technical requirements need to be ≤0.02mV / h, weight level is 1), constant current ratio difference (technical requirements need to be ≤≤1.0%, weight level is 2), residual capacity difference (technical requirements need to be ≤1.0%, weight level is 1), platform capacity weight (technical requirements need to be ≤2%, weight level is 1), and open circuit voltage difference (technical requirements need to be ≤5-10mV, weight level is 2).

[0078] In a specific implementation, the electrical parameters of the battery cells during operation are tested to obtain the test results of the battery cells. The battery cells of different grades are screened based on the test results. When the parameters between the battery cells of different grades meet the preset standards, the battery cells of different grades are grouped to improve the voltage consistency of the battery cell modules of different grades.

[0079] Furthermore, if Fig.10 As shown, the step S30 specifically includes:

[0080] Step S31: When the residual capacity, constant current ratio, self-discharge K value, AC impedance, open circuit voltage difference and platform capacity ratio weight of each level of battery cells meet the preset standards, the battery cells of each level are grouped.

[0081] In a specific implementation, when each level of battery cells meets the preset standards, the battery cells of each level are grouped and can be placed in the same level of battery cell modules.

[0082] Based on the first embodiment of the present application, in the second embodiment of the present application, the same or similar contents as those in the first embodiment can refer to the above introduction, and will not be repeated in the following. Figure 2 , Figure 2 This is a flow chart of a second embodiment of the method for dividing and grouping lithium iron phosphate batteries for cascade utilization proposed in an embodiment of the present application.

[0083] Considering the cascade utilization of retired batteries, in order to select the cascade batteries, such as Figure 2 and Fig.11 As shown, step S10 in this embodiment specifically includes:

[0084] Step S11: performing a capacity test on the battery cell to determine the residual capacity, constant current ratio, recovery voltage, platform capacity ratio and platform capacity ratio weight of the battery cell.

[0085] Step S12: performing an aging test on the battery cell to determine the self-discharge K value of the battery cell.

[0086] Step S13: performing internal resistance and open circuit voltage tests on the battery cell to determine the AC impedance and open circuit voltage of the battery cell.

[0087] It should be noted that the cell capacity test is to perform charge and discharge tests on the disassembled cells, classify them according to parameters such as capacity and internal resistance, and combine batteries with similar performance for subsequent applications. The cell aging test is designed to evaluate the performance changes of the cells under long-term use or under specific conditions, which helps to understand the life, stability and performance of the cells under different conditions.

[0088] In a specific implementation, a capacity test is performed on the battery cell to determine the residual capacity, constant current ratio, recovery voltage, platform capacity ratio and platform capacity ratio weight of the battery cell; an aging test is performed on the battery cell to determine the self-discharge K value of the battery cell; an internal resistance and open circuit voltage test is performed on the battery cell to determine the AC impedance and open circuit voltage of the battery cell, thereby obtaining the test results of the battery cell and further realizing the screening of tiered battery cells.

[0089] Furthermore, if Figure 8 As shown, the step S12 specifically includes:

[0090] Step S121: performing an aging test when the capacity of the battery cell is the eighth cutoff capacity.

[0091] Step S122: Determine the test conditions of the aging test according to the aging test requirements.

[0092] Step S123: performing an aging test on the battery cell according to the test conditions, and determining the voltage of the battery cell before and after the aging test.

[0093] Step S124: determining the self-discharge K value of the battery cell according to the voltage before and after the battery cell aging test and the aging test temperature.

[0094] It should be noted that the eighth cut-off capacity is C8, and the test conditions of the aging test include high temperature aging temperature, high temperature aging time, room temperature aging temperature, room temperature aging time H (unit: hour), open circuit voltage OCV1 before room temperature aging, open circuit voltage OCV2 after room temperature aging, and the self-discharge K value of the battery cell can be expressed as:

[0095] K=(OCV1-OCV2) / H

[0096] In the specific implementation, when the battery cell self-discharge K value test (aging test) is conducted, the battery cell standby capacity (eighth cutoff capacity) C8 is specified to be in the range of 1% to 10%, the high temperature aging temperature is 45±2°C, the high temperature aging time is 72h, the normal temperature aging temperature is 25±2°C, and the normal temperature aging time is 3 to 5 days.

[0097] Based on the second embodiment of the present application, in the third embodiment of the present application, the same or similar contents as those of the second embodiment can be referred to the above introduction, and will not be repeated in the following. Figure 3 , Figure 3 This is a flow chart of a third embodiment of the method for dividing and grouping lithium iron phosphate batteries for cascade utilization proposed in an embodiment of the present application.

[0098] Considering that the internal polarization resistance of the battery cell can be measured by the platform capacity ratio and the rebound voltage method, the DC internal resistance test items can be reduced, and then in order to determine the discharge capacity and charge capacity of the battery cell, such as Figure 3 As shown, step S11 in this embodiment specifically includes:

[0099] Step S111: charging the battery cell with a first current until a first voltage is reached, and determining the charging capacity of the battery cell.

[0100] Step S112: discharging the battery cell with a first current until a second voltage is reached, and determining a discharge capacity of the battery cell.

[0101] Step S113: determining the residual capacity, constant current ratio, recovery voltage, platform capacity ratio and platform capacity ratio weight of the battery cell according to the first voltage, the second voltage, the charging capacity and the discharging capacity.

[0102] It should be noted that the first current is I, the first voltage and the second voltage can be set according to the termination voltage of the battery cell, and this embodiment is not limited thereto. The termination voltage of charging / discharging refers to the highest / lowest voltage value reached by the battery during the charging / discharging process. At this time, charging / discharging should be stopped to prevent overcharging / over-discharging of the battery.

[0103] In a specific implementation, the battery cell is charged by a first current to a first voltage, and the charging capacity of the battery cell is determined; the battery cell is discharged by the first current to a second voltage, and the discharge capacity of the battery cell is determined; and according to the first voltage, the second voltage, the charging capacity and the discharging capacity, the residual capacity, constant current ratio, recovery voltage, platform capacity ratio and platform capacity ratio weight of the battery cell are determined, thereby realizing the screening of tiered battery cells.

[0104] Furthermore, if Fig. 9 As shown, the step S113 specifically includes:

[0105] Step S1131: determining the residual capacity of the battery cell according to the fourth discharge capacity, the fifth discharge capacity, the sixth discharge capacity and the seventh discharge capacity.

[0106] Step S1132: determining a constant current ratio of the battery cell according to the first charging capacity, the second charging capacity and the third charging capacity.

[0107] Step S1133: determining the recovery voltage of the battery cell according to the fifth termination voltage and the sixth termination voltage.

[0108] Step S1134: Determine the platform capacity ratio and the platform capacity ratio weight according to the charging capacity and the discharging capacity.

[0109] It should be noted that the first charging capacity, the second charging capacity, the third charging capacity, the fourth discharging capacity, the fifth discharging capacity, the sixth discharging capacity and the seventh discharging capacity are respectively: C1~C7, the first termination voltage to the sixth termination voltage are respectively: V1~V6, the residual capacity C=C4+C5+C6+C7, the constant current ratio=C3 / (C1+C2+C3)*100%, the recovery voltage ΔV=V6-V5, the V1 platform capacity ratio γ1=C1 / C*100%, the V3 platform capacity ratio γ2=C4 / C*100%, the V4 platform capacity ratio γ3=(C4+C5) / C*100%, the V5 platform capacity ratio γ4=(C4+C5+C6) / C*100%, and the platform capacity ratio weight η=γ1*γ2*γ3*γ4.

[0110] In a specific implementation, the residual capacity of the battery cell is determined according to the fourth discharge capacity, the fifth discharge capacity, the sixth discharge capacity and the seventh discharge capacity, the constant current ratio of the battery cell is determined according to the first charging capacity, the second charging capacity and the third charging capacity, the recovery voltage of the battery cell is determined according to the fifth termination voltage and the sixth termination voltage, and the platform capacity ratio and the platform capacity ratio weight are determined according to the charging capacity and the discharging capacity, so as to obtain the test results of the battery cell, and then realize the screening of tiered battery cells.

[0111] Based on the third embodiment of the present application, in the fourth embodiment of the present application, the same or similar contents as those in the third embodiment can refer to the above introduction, and will not be repeated in the following. Figure 4 , Figure 4 This is a flow chart of a fourth embodiment of the method for dividing and grouping lithium iron phosphate batteries for cascade utilization proposed in an embodiment of the present application.

[0112] Considering that the battery cell is charged and discharged at constant current and constant voltage, in order to determine the discharge capacity and charge capacity of the battery cell, such as Figure 4 As shown, step S111 in this embodiment specifically includes:

[0113] Step S1111: performing constant current charging on the battery cell by using a first current until a first termination voltage is reached, and determining a first charging capacity of the battery cell.

[0114] Step S1112: performing constant current charging on the battery cell by using a first current until a second termination voltage is reached, and determining a second charging capacity of the battery cell.

[0115] Step S1113: performing constant voltage charging on the battery cell using the first current until a second termination voltage and a second termination current are reached, and determining a third charging capacity of the battery cell.

[0116] It should be noted that a preset time needs to be set before step S1111 is performed. The preset time can be 30 minutes, or it can be set according to actual conditions. This embodiment does not limit this. The first current is I, and the termination current is 0.05I 10 , the size of I is 0.5~1.0I 10 .

[0117] In the specific implementation, the battery cell is charged with a constant current of I to a first termination voltage V1, and the first charging capacity is recorded as C1, where the voltage range of V1 is 3.30~3.50V; the battery cell is charged with a constant current of I to a second termination voltage V2, and the second charging capacity is recorded as C2, where the voltage range of V2 is 3.5~3.65V; the battery cell is charged with a constant voltage of I to a second termination voltage V2, and the termination current is 0.05I 10 , the third charging capacity is recorded as C3.

[0118] Furthermore, if Figure 5 As shown, the step S112 specifically includes:

[0119] Step S1121: performing constant current discharge on the battery cell using a first current until a third termination voltage is reached, and determining a fourth discharge capacity of the battery cell.

[0120] Step S1122: performing constant current discharge on the battery cell using the first current until a fourth termination voltage is reached, and determining a fifth discharge capacity of the battery cell.

[0121] Step S1123: performing constant current discharge on the battery cell by using the first current until a fifth termination voltage is reached, and determining a sixth discharge capacity of the battery cell.

[0122] It should be noted that a preset time needs to be left before performing step S1121. The preset time may be 30 minutes, or may be set according to actual conditions, and this embodiment does not limit this.

[0123] In the specific implementation, the battery cell is discharged with a constant current I to a third termination voltage V3, and the fourth discharge capacity is recorded as C4, where the voltage range of V3 is 3.15~3.25V; the battery cell is discharged with a constant current I to a fourth termination voltage V4, and the fifth discharge capacity is recorded as C5, where the voltage range of V4 is 2.8~3.15V; the battery cell is discharged with a constant current I to a fifth termination voltage V5, and the sixth discharge capacity is recorded as C6, where the voltage range of V5 is 2.50~2.80V.

[0124] Furthermore, considering the discharge performance of the battery cell, such as Figure 6 As shown, before step S111, the following steps are also included:

[0125] Step S11101: discharging the battery cell with a first current until a preset first voltage is reached.

[0126] Step S11102: discharging the battery cell from the preset first voltage to a preset second voltage through a second current.

[0127] It should be noted that the preset first voltage may be 2.5V, the preset second voltage may be 2.0V, and the preset first voltage and the preset second voltage may also be set according to the type of battery cell, which is not limited in this embodiment.

[0128] In the specific implementation, the battery cell is first discharged to 2.5V with a constant current of I, and then discharged with a current of 0.05I 10 Discharge at constant current to 2.0V.

[0129] Furthermore, considering that the internal polarization resistance of the battery cell can be measured by determining the rebound voltage method, the DC internal resistance test items can be reduced, such as Figure 7 As shown, after step S112, the following further includes:

[0130] Step S11201: After the battery cell is left alone for a preset first time, a sixth termination voltage of the last preset second time is collected.

[0131] Step S11202: discharging the battery cell with a second current until a seventh termination voltage, and determining a seventh discharge capacity of the battery cell.

[0132] Step S11203: charging the battery cell with the first current until a preset third voltage is reached, and determining an eighth cutoff capacity of the battery cell.

[0133] It should be noted that the preset first time can be 30 minutes, the preset second time can be 1 second, and the preset third voltage can be 3.4V. The preset first time, the preset second time, and the preset third voltage can also be set according to test requirements, and this embodiment is not limited.

[0134] In the specific implementation, the battery cell is left for 30 minutes, and the voltage collected in the last 1 second is recorded as V6 (the sixth termination voltage); 10 The battery is discharged at a constant current to the seventh termination voltage V7, and the seventh charging capacity is recorded as C7, where the voltage range of V7 is 1.8-2.50V; after being left alone for 30 minutes again, the battery is charged at a constant current I to 3.4V, and the eighth cut-off capacity is C8, where the range of C8 is 1%-10% of the rated capacity.

[0135] The above are only preferred embodiments of the present application, and are not intended to limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A method for dividing and grouping lithium iron phosphate batteries for cascade utilization, characterized in that: The method for dividing and grouping lithium iron phosphate batteries for cascade utilization includes: Testing the electrical parameters of the battery cell during operation to obtain the test results of the battery cell; According to the test results, the battery cells are screened; When various parameters between battery cells of different levels meet the preset standards, the battery cells of different levels are grouped.

2. The method for dividing and grouping lithium iron phosphate batteries for cascade utilization according to claim 1, characterized in that: The electrical parameters include: residual capacity, constant current ratio, recovery voltage, platform capacity ratio, platform capacity ratio weight, self-discharge K value, AC impedance and open circuit voltage; The step of testing the electrical parameters of the battery cell during operation to obtain the test result of the battery cell specifically includes: Performing a capacity test on the battery cell to determine the residual capacity, constant current ratio, recovery voltage, platform capacity ratio and platform capacity ratio weight of the battery cell; Performing an aging test on the battery cell to determine the self-discharge K value of the battery cell; Perform internal resistance and open circuit voltage tests on the battery cell to determine the AC impedance and open circuit voltage of the battery cell.

3. The method for dividing and grouping lithium iron phosphate batteries for cascade utilization according to claim 2, characterized in that: The step of performing a capacity test on the battery cell to determine the residual capacity, constant current ratio, recovery voltage, platform capacity ratio and platform capacity ratio weight of the battery cell specifically includes: charging the battery cell to a first voltage using a first current and determining a charge capacity of the battery cell; discharging the battery cell by a first current to a second voltage, and determining a discharge capacity of the battery cell; The residual capacity, constant current ratio, recovery voltage, platform capacity ratio and platform capacity ratio weight of the battery cell are determined according to the first voltage, the second voltage, the charging capacity and the discharging capacity.

4. The method for dividing and grouping lithium iron phosphate batteries for cascade utilization according to claim 3, characterized in that: The step of charging the battery cell by the first current to a first voltage and determining the charging capacity of the battery cell specifically includes: Performing constant current charging on the battery cell by a first current until a first termination voltage is reached, and determining a first charging capacity of the battery cell; Performing constant current charging on the battery cell by using a first current until a second termination voltage is reached, and determining a second charging capacity of the battery cell; The battery cell is charged at a constant voltage by a first current until a second termination voltage and a second termination current are reached, and a third charging capacity of the battery cell is determined.

5. The method for dividing and grouping lithium iron phosphate batteries for cascade utilization according to claim 4, characterized in that: The step of discharging the battery cell by the first current until the second voltage is reached and determining the discharge capacity of the battery cell specifically includes: Discharging the battery cell at a constant current by a first current until a third termination voltage is reached, and determining a fourth discharge capacity of the battery cell; Discharging the battery cell at a constant current by a first current until a fourth termination voltage is reached, and determining a fifth discharge capacity of the battery cell; The battery cell is discharged at a constant current by using a first current until a fifth termination voltage, and a sixth discharge capacity of the battery cell is determined.

6. The method for dividing and grouping lithium iron phosphate batteries for cascade utilization according to claim 3, characterized in that: Before the step of charging the battery cell by the first current to a first voltage and determining the charging capacity of the battery cell, the method further includes: Discharging the battery cell by a first current until a preset first voltage is reached; The battery cell is discharged from the preset first voltage to a preset second voltage through a second current.

7. The method for dividing and grouping lithium iron phosphate batteries for cascade utilization according to claim 5, characterized in that: After the step of discharging the battery cell by the first current until the second voltage is reached and determining the discharge capacity of the battery cell, the method further includes: After the battery cell is left idle for a preset first time, a sixth termination voltage of the last preset second time is collected; discharging the battery cell by a second current until a seventh termination voltage, and determining a seventh discharge capacity of the battery cell; The battery cell is charged by the first current until a preset third voltage is reached, and an eighth cutoff capacity of the battery cell is determined.

8. The method for dividing and grouping lithium iron phosphate batteries for cascade utilization according to claim 7, characterized in that: The step of performing an aging test on the battery cell to determine the self-discharge K value of the battery cell specifically includes: Performing an aging test when the capacity of the battery cell is an eighth cutoff capacity; Determine the test conditions of the aging test according to the aging test requirements; Performing an aging test on the battery cell according to the test conditions, and determining the voltage of the battery cell before and after the aging test; The self-discharge K value of the battery cell is determined according to the voltage before and after the battery cell aging test and the aging test temperature.

9. The method for dividing and grouping lithium iron phosphate batteries for cascade utilization according to claim 8, characterized in that: The step of determining the residual capacity, constant current ratio, recovery voltage, platform capacity ratio and platform capacity ratio weight of the battery cell according to the first voltage, the second voltage, the charging capacity and the discharging capacity specifically includes: determining a residual capacity of the battery cell according to the fourth discharge capacity, the fifth discharge capacity, the sixth discharge capacity, and the seventh discharge capacity; Determining a constant current ratio of the battery cell according to the first charging capacity, the second charging capacity and the third charging capacity; Determining a recovery voltage of the battery cell according to the fifth termination voltage and the sixth termination voltage; According to the charging capacity and the discharging capacity, the platform capacity ratio and the platform capacity ratio weight are determined.

10. The method for dividing and grouping lithium iron phosphate batteries for cascade utilization according to claim 2, characterized in that: When the parameters of the battery cells of different levels meet the preset standards, the step of grouping the battery cells of different levels specifically includes: When the residual capacity, constant current ratio, self-discharge K value, AC impedance, open circuit voltage difference and platform capacity ratio weight of each tier of battery cells meet the preset standards, the battery cells of each tier are grouped.

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