Lithium iron phosphate battery capacity grading method and lithium iron phosphate battery pack

Abstract

The invention relates to a lithium iron phosphate battery capacity grading method and a lithium iron phosphate battery pack. The lithium iron phosphate battery capacity grading method specifically comprises the following steps: charging a battery to be processed to a first rated voltage and a first cut-off current according to a first current rate; carrying out first shelving treatment on the battery which is charged for the first time; discharging the battery subjected to the first shelving treatment to a second rated voltage according to a second current rate; carrying out second shelving treatment on the battery which is discharged for the first time; and discharging the battery subjected to the second shelving treatment to a second rated voltage according to a third current rate. According to the capacity grading method provided by the invention, different charge-discharge multiplying powers are set in the capacity grading process, and the synergistic effect of different multiplying powers on polarization elimination in the charge-discharge process is exerted, so that the capacity grading capacity reaches the real capacity of the battery cell, the battery cell capacity matching use can be directly carried out, the construction period is shortened to a relatively high degree, the production efficiency is improved, and the production cost is reduced. And the whole process is carried out at room temperature, so that the safety of the process is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a lithium iron phosphate battery capacity division method and a lithium iron phosphate battery pack. Background Art

[0002] The development of new energy vehicles has become an important strategic measure to address climate change and promote green development. Low-carbon and environmentally friendly electric public transportation is becoming more and more popular in large and medium-sized cities, and green means of transportation such as electric cars are also gradually becoming popular among individual consumers. Lithium batteries have become the first choice for providing power for green travel tools due to their high specific energy, long cycle life, high safety performance and low environmental pollution.

[0003] As a power source for electric bicycles, electric motorcycles, electric vehicles, aerospace, and power storage, lithium batteries require excellent energy density, high and low temperature discharge, rate, and cycle performance. In addition, ensuring the consistency of lithium batteries is also crucial, because lithium batteries, as a power source for transportation and power storage, often require dozens, hundreds, or even thousands of cells to be connected in series and parallel to ensure the driving range. In order to avoid the "short board effect" caused by inconsistent capacity of the cells connected in series during the normal charging and discharging process of the module, which causes some cells to be overcharged or over-discharged, resulting in battery fires, explosions, and other safety accidents, companies need to reduce production costs and improve production efficiency while also minimizing the capacity differences between battery packs.

[0004] Since the solid-phase diffusion rate of lithium ions in lithium battery positive electrode materials is low and the primary particle size distribution of positive electrode materials is large, the primary particles are more polarized than most active materials, resulting in the inability of lithium ions to fully escape during the first cycle of charge and discharge. Therefore, the first cycle of capacity division is usually not the actual capacity of a single battery. If the first cycle of capacity division is used for shipping capacity matching, it is easy to cause a "short board effect". In order to eliminate the impact of inconsistent capacity of offline cells caused by polarization, most battery manufacturers usually use multiple capacity division processes or small current capacity division processes.

[0005] In order to ensure that the capacity of the cell off the line is the real capacity of the cell, the current multi-charge capacity division process is mostly used, or the low-rate current capacity division process is used. The multi-charge capacity division process takes 6 to 12 hours more than the single capacity division process, and the low-current rate capacity division process only takes 10 hours for one discharge. For example, the invention patent application with publication number CN116613399A discloses a capacity division method and battery, which achieves the activation effect of the battery by performing charging steps, static steps, and discharging steps multiple times, but the capacity division process is time-consuming, and the low capacity division efficiency increases the production cost of the enterprise. Summary of the invention

[0006] The object of the present invention is to provide a lithium iron phosphate battery capacity division method and a lithium iron phosphate battery pack. By setting different charge and discharge rates during the capacity division process, the synergistic effect of different rates in the charge and discharge process on eliminating polarization is brought into play, so that lithium ions can be fully released from the positive electrode material and embedded in the graphite, and the negative electrode graphite can release enough lithium ions to be embedded back in the positive electrode material during discharge, so that the divided capacity reaches the real capacity of the battery cell, and the battery cell capacity can be directly grouped for use, which greatly reduces the capacity division time, improves production efficiency, and reduces production costs.

[0007] The present invention solves the above technical problems in the following way: A lithium iron phosphate battery capacity division method comprises the following steps:

[0008] 1) charging the battery to be processed at a first current rate to a first rated voltage and a first cut-off current;

[0009] 2) performing a first storage treatment on the battery that has completed the first charging;

[0010] 3) discharging the battery that has completed the first standby treatment to a second rated voltage according to a second current rate;

[0011] 4) performing a second storage treatment on the battery that has completed the first discharge;

[0012] 5) Discharging the battery after the second standby treatment to the second rated voltage according to the third current rate.

[0013] Preferably, during the capacity division process, the ambient temperature of the battery is 23-27°C.

[0014] Preferably, in step 1), the first current ratio is 0.1-3C.

[0015] Preferably, in step 1), the first rated voltage is 3.65V and the first cut-off current is 0.05C.

[0016] Preferably, in step 2), the first holding treatment time is 10 to 30 minutes.

[0017] Preferably, in step 3), the ratio of the second current magnification to the first current magnification is 0.5-2.

[0018] Preferably, in step 3), the second rated voltage is 2.5V.

[0019] Preferably, the ratio of the second suspension processing time to the first suspension processing time is 0.1 to 0.4.

[0020] Preferably, the ratio of the third current magnification to the second current magnification is 0.05-1.

[0021] The purpose of taking this step is that the battery itself has internal resistance (including ohmic polarization and electrochemical polarization). Therefore, polarization will occur as long as the battery is energized. When the lithium ions released from the negative electrode pass through the electrolyte area, they remain in the electrolyte area due to the cessation of current. In order to eliminate the polarization of the second step of discharge, the third current rate is designed to be a low proportional value of the second current rate, so that the lithium ions remaining in the electrolyte area can enter the positive electrode.

[0022] A lithium iron phosphate battery pack is obtained by classifying and combining a plurality of lithium iron phosphate batteries according to the method described above.

[0023] The beneficial effects of the present invention are as follows:

[0024] The lithium iron phosphate battery capacity division method provided by the present invention sets different current rates in different charge and discharge stages to eliminate the synergistic effect of polarization so that lithium ions can be fully released from the positive electrode material and embedded in graphite, and the negative electrode graphite can release enough lithium ions to be embedded back in the positive electrode material during discharge, so that the divided capacity reaches the real capacity of the battery cell, and the battery cell capacity can be directly grouped for use, which is convenient for shipment and direct capacity grading and grouping at the module PACK end, greatly reducing the capacity division time, improving production efficiency, and reducing production costs.

[0025] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the preferred embodiments of the present invention are described in detail below. The specific implementation of the present invention is given in detail by the following embodiments. DETAILED DESCRIPTION

[0026] The principles and features of the present invention are described below in conjunction with embodiments. The examples given are only used to explain the present invention and provide a further understanding of the present invention, constitute a part of this application, and are not used to limit the scope of the present invention.

[0027] The following embodiments and comparative examples all use 207Ah lithium iron phosphate batteries of the same batch and specification for capacity separation.

[0028] Example 1

[0029] This embodiment adopts the following steps to perform capacity division processing on the lithium iron phosphate battery, and the ambient temperature of the entire capacity division process is maintained at 25±2°C:

[0030] 1) Charge the battery to be treated at 0.3C constant current and constant voltage to 3.65V, with a cut-off current of 0.05C;

[0031] 2) Leave the battery that has completed the first charge for 30 minutes;

[0032] 3) discharging the battery after the step 2) to 2.5V at a constant current and constant voltage of 0.5C;

[0033] 4) The battery discharged in step 3) is left for 10 minutes;

[0034] 5) The battery that has completed the standby treatment in step 4) is discharged at a constant current and constant voltage of 0.1C to 2.5V.

[0035] The capacity of each discharge and the total discharge time were recorded, and the results are shown in Table 1. To confirm whether the cell capacity has been fully utilized after this capacity division, the above capacity division steps were repeated 3 times after the end of this capacity division and the discharge capacity of each capacity division was recorded. The results are shown in Table 2.

[0036] Example 2

[0037] This embodiment adopts the following steps to perform capacity division processing on the lithium iron phosphate battery, and the ambient temperature of the entire capacity division process is maintained at 25±2°C:

[0038] 1) Charge the battery to be treated to 3.65V at 0.5C constant current and constant voltage, with a cut-off current of 0.05C;

[0039] 2) Leave the battery that has completed the first charge for 30 minutes;

[0040] 3) discharging the battery after the step 2) to 2.5V at a constant current and constant voltage of 0.5C;

[0041] 4) The battery discharged in step 3) is left for 10 minutes;

[0042] 5) The battery that has completed the standby treatment in step 4) is discharged at a constant current and constant voltage of 0.1C to 2.5V.

[0043] The capacity of each discharge and the total discharge time were recorded, and the results are shown in Table 1. To confirm whether the cell capacity has been fully utilized after this capacity division, the above capacity division steps were repeated 3 times after the end of this capacity division and the discharge capacity of each capacity division was recorded. The results are shown in Table 2.

[0044] Example 3

[0045] This embodiment adopts the following steps to perform capacity division processing on the lithium iron phosphate battery, and the ambient temperature of the entire capacity division process is maintained at 25±2°C:

[0046] 1) Charge the battery to be treated to 3.65V at 0.5C constant current and constant voltage, with a cut-off current of 0.05C;

[0047] 2) Leave the battery that has completed the first charge for 30 minutes;

[0048] 3) discharging the battery after the step 2) to 2.5V at a constant current and constant voltage of 0.3C;

[0049] 4) The battery discharged in step 3) is left for 10 minutes;

[0050] 5) The battery that has completed the standby treatment in step 4) is discharged at a constant current and constant voltage of 0.1C to 2.5V.

[0051] The capacity of each discharge and the total discharge time were recorded, and the results are shown in Table 1. To confirm whether the cell capacity has been fully utilized after this capacity division, the above capacity division steps were repeated 3 times after the end of this capacity division and the discharge capacity of each capacity division was recorded. The results are shown in Table 2.

[0052] Example 4

[0053] This embodiment adopts the following steps to perform capacity division processing on the lithium iron phosphate battery, and the ambient temperature of the entire capacity division process is maintained at 25±2°C:

[0054] 1) Charge the battery to be treated at 1.0C constant current and constant voltage to 3.65V, with a cut-off current of 0.05C;

[0055] 2) Leave the battery that has completed the first charge for 30 minutes;

[0056] 3) discharging the battery after the step 2) to 2.5V at a constant current and constant voltage of 1.0C;

[0057] 4) The battery discharged in step 3) is left for 10 minutes;

[0058] 5) The battery that has completed the standby treatment in step 4) is discharged at a constant current and constant voltage of 0.1C to 2.5V.

[0059] The capacity of each discharge and the total discharge time were recorded, and the results are shown in Table 1. To confirm whether the cell capacity has been fully utilized after this capacity division, the above capacity division steps were repeated 3 times after the end of this capacity division and the discharge capacity of each capacity division was recorded. The results are shown in Table 2.

[0060] Example 5

[0061] This embodiment adopts the following steps to perform capacity division processing on the lithium iron phosphate battery, and the ambient temperature of the entire capacity division process is maintained at 25±2°C:

[0062] 1) Charge the battery to be treated at 0.3C constant current and constant voltage to 3.65V, with a cut-off current of 0.05C;

[0063] 2) Leave the battery that has completed the first charge for 30 minutes;

[0064] 3) discharging the battery after the step 2) to 2.5V at a constant current and constant voltage of 0.3C;

[0065] 4) The battery discharged in step 3) is left for 10 minutes;

[0066] 5) The battery that has completed the standby treatment in step 4) is discharged at a constant current and constant voltage of 0.1C to 2.5V.

[0067] The capacity of each discharge and the total discharge time were recorded, and the results are shown in Table 1. To confirm whether the cell capacity has been fully utilized after this capacity division, the above capacity division steps were repeated 3 times after the end of this capacity division and the discharge capacity of each capacity division was recorded. The results are shown in Table 2.

[0068] Comparative Example 1

[0069] This comparative example adopts the following steps to process the lithium iron phosphate battery, and the ambient temperature of the entire capacity division process is maintained at 25±2℃:

[0070] 1) Charge the battery to be treated to 3.65V at 0.5C constant current and constant voltage, with a cut-off current of 0.05C;

[0071] 2) Leave the battery that has completed the first charge for 30 minutes;

[0072] 3) The battery that has completed the standby treatment in step 2) is discharged at a constant current and constant voltage of 0.5C to 2.5V.

[0073] The capacity of each discharge and the total discharge time were recorded, and the results are shown in Table 1. To confirm whether the cell capacity has been fully utilized after this capacity division, the above capacity division steps were repeated 3 times after the end of this capacity division and the discharge capacity of each capacity division was recorded. The results are shown in Table 2.

[0074] Comparative Example 2

[0075] This comparative example adopts the following steps to process the lithium iron phosphate battery, and the ambient temperature of the entire capacity division process is maintained at 25±2℃:

[0076] 1) Charge the battery to be treated at 1.0C constant current and constant voltage to 3.65V, with a cut-off current of 0.05C;

[0077] 2) Leave the battery that has completed the first charge for 30 minutes;

[0078] 3) The battery that has completed the standby treatment in step 2) is discharged at a constant current and constant voltage of 1.0C to 2.5V.

[0079] The capacity of each discharge and the total discharge time were recorded, and the results are shown in Table 1. To confirm whether the cell capacity has been fully utilized after this capacity division, the above capacity division steps were repeated 3 times after the end of this capacity division and the discharge capacity of each capacity division was recorded. The results are shown in Table 2.

[0080] Comparative Example 3

[0081] This comparative example adopts the following steps to process the lithium iron phosphate battery, and the ambient temperature of the entire capacity division process is maintained at 25±2℃:

[0082] 1) Charge the battery to be treated to 3.65V at a constant current and constant voltage of 0.1C, with a cut-off current of 0.05C;

[0083] 2) Leave the battery that has completed the first charge for 30 minutes;

[0084] 3) The battery that has completed the standby treatment in step 2) is discharged at a constant current and constant voltage of 0.1C to 2.5V.

[0085] The capacity of each discharge and the total discharge time were recorded, and the results are shown in Table 1. To confirm whether the cell capacity has been fully utilized after this capacity division, the above capacity division steps were repeated 3 times after the end of this capacity division and the discharge capacity of each capacity division was recorded. The results are shown in Table 2.

[0086] Comparative Example 4

[0087] This comparative example adopts the following steps to process the lithium iron phosphate battery, and the ambient temperature of the entire capacity division process is maintained at 25±2℃:

[0088] 1) Charge the battery to be treated to 3.65V at 0.5C constant current and constant voltage, with a cut-off current of 0.05C;

[0089] 2) Leave the battery that has completed the first charge for 30 minutes;

[0090] 3) Discharge the battery after the above-mentioned storage treatment at a constant current and constant voltage of 0.5C to 2.5V;

[0091] 4) Leave the battery that has completed the first discharge for 30 minutes;

[0092] 5) The battery that has completed the above-mentioned storage treatment is charged to 3.65V at a constant current and constant voltage of 0.5C, and the cut-off current is 0.05C;

[0093] 6) Leave the battery that has completed the second charge for 30 minutes;

[0094] 7) Discharge the battery after the above-mentioned storage treatment at a constant current and constant voltage of 0.5C to 2.5V;

[0095] 8) Leave the battery that has completed the second discharge for 30 minutes;

[0096] 9) The battery that has completed the above-mentioned storage treatment is charged to 3.65V at a constant current and constant voltage of 0.5C, and the cut-off current is 0.05C;

[0097] 10) Leave the battery after the third charge for 30 minutes;

[0098] 11) Discharge the battery after the above-mentioned storage treatment at a constant current and constant voltage of 0.5C to 2.5V;

[0099] 12) The battery that has completed the third discharge is left alone for 30 minutes;

[0100] 13) The battery that has completed the above-mentioned storage treatment is charged to 3.65V at a constant current and constant voltage of 0.5C, and the cut-off current is 0.05C;

[0101] 14) Leave the battery after the fourth charge for 30 minutes;

[0102] 15) The battery that has completed the above-mentioned storage treatment is discharged at a constant current and constant voltage of 0.5C to 2.5V.

[0103] Comparative Example 5

[0104] This comparative example adopts the following steps to process the lithium iron phosphate battery, and the ambient temperature of the entire capacity division process is maintained at 45±2℃:

[0105] 1) Charge the battery to be treated to 3.65V at 0.5C constant current and constant voltage, with a cut-off current of 0.05C;

[0106] 2) Leave the battery that has completed the first charge for 30 minutes;

[0107] 3) The battery that has completed the above-mentioned storage treatment is discharged at a constant current and constant voltage of 0.5C to 2.5V.

[0108] The capacity of each discharge and the total discharge time were recorded, and the results are shown in Table 1. To confirm whether the cell capacity has been fully utilized after this capacity division, the above capacity division steps were repeated 3 times after the end of this capacity division and the discharge capacity of each capacity division was recorded. The results are shown in Table 2.

[0109] Table 1 Capacity of each embodiment and comparative example after each discharge

[0110]

[0111] From Example 1 to Example 5 in Table 1, it is found that the charging capacity cannot be completely released after the first discharge. It can be found in Example 4 and Comparative Example 2 that by increasing the second discharge (0.1C), the capacity division time is only increased by 15min, and the capacity of a single battery cell can be increased by 1.3Ah. After the first stage of capacity division discharge to 2.5V, a small current discharge is added; it helps to eliminate polarization, so that the lithium ions embedded in the graphite are fully released, and the discharge capacity of the battery cell is closer to the capacity of the battery cell itself. Comparing Example 4 and Example 5, simply reducing the charge and discharge rate can further reduce polarization and exert the actual capacity of the battery cell, but after the charge and discharge rate is reduced from 1C to 0.3C, the overall capacity division time is greatly increased, from the original 140min to 390min. By comparing Example 1, Example 2 and Example 3, it is found that by reducing the charge and discharge rate of the capacity division, and coordinating the charge and discharge rate, the synergistic effect of different rates on polarization elimination during the charge and discharge process is brought into play. When charging to 3.65V at a low rate of 0.3C, polarization has little effect on the charge capacity, and lithium ions can be fully removed from the positive electrode material and embedded in graphite. The first step of the discharge current is increased to 0.5C, which can significantly reduce the production time (Example 1 vs. Example 5), improve production efficiency, and reduce production costs. Although the time of Example 1 is shorter than that of Example 1, the capacity of the cell capacity division is quite different from the actual capacity of the cell itself. If the capacity is divided and grouped, the value of the product itself is wasted, and in the later use process, the capacity after polarization elimination plays out the actual value of the cell itself, which will greatly affect the BMS control effect. Although the capacity division process of Example 3, Example 4 and Example 5 can play out the actual capacity of the cell itself, the process is too time-consuming, or the energy consumption is too large, and the production cost is greatly increased, and the products produced are not competitive.

[0112] Table 2 Capacity of each embodiment and comparative example after repeated operation

[0113]

[0114]

[0115] From the verification results in Table 2, it can be seen that reducing the charge and discharge rate during the capacity division process, or increasing the number of charge and discharge cycles during the capacity division process can release the real capacity of the battery cell, but simply reducing the rate or simply increasing the number of cycles greatly reduces the production efficiency of the enterprise. Through Example 1, Example 5, Comparative Example 3, Comparative Example 4, and Comparative Example 5, the real capacity value of the battery cell itself can be reached after the first capacity division is completed, and by coordinating and utilizing the charge and discharge rates at different stages in the capacity division process, the synergistic effect of different rates in the charge and discharge process on eliminating polarization is exerted, and the discharge capacity after the first capacity division can reach the real capacity of the battery cell.

[0116] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any ordinary technician in the industry can smoothly implement the present invention as shown in the specification and described above. However, any equivalent changes, modifications and evolutions made by technicians familiar with the profession without departing from the scope of the technical solution of the present invention using the technical content disclosed above are all equivalent embodiments of the present invention. At the same time, any equivalent changes, modifications and evolutions made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the technical solution of the present invention.

Claims

1. A lithium iron phosphate battery capacity division method, characterized in that: The following steps are involved: 1) charging the battery to be processed at a first current rate to a first rated voltage and a first cut-off current; 2) performing a first storage treatment on the battery that has completed the first charging; 3) discharging the battery that has completed the first standby treatment to a second rated voltage according to a second current rate; 4) performing a second storage treatment on the battery that has completed the first discharge; 5) Discharging the battery after the second standby treatment to the second rated voltage according to the third current rate.

2. A lithium iron phosphate battery capacity division method as claimed in claim 1, characterized in that: During the capacity division process, the ambient temperature of the battery is 23-27°C.

3. A lithium iron phosphate battery capacity division method as claimed in claim 1, characterized in that: In the step 1), the first current ratio is 0.1 to 3C.

4. A lithium iron phosphate battery capacity division method as claimed in claim 1, characterized in that: In the step 1), the first rated voltage is 3.65V, and the first cut-off current is 0.05C.

5. A lithium iron phosphate battery capacity division method as claimed in claim 1, characterized in that: In the step 2), the first holding treatment time is 10 to 30 minutes.

6. A lithium iron phosphate battery capacity division method as claimed in claim 1, characterized in that: In the step 3), the ratio of the second current magnification to the first current magnification is 0.5-2.

7. A lithium iron phosphate battery capacity division method as claimed in claim 1, characterized in that: In the step 3), the second rated voltage is 2.5V.

8. A lithium iron phosphate battery capacity division method as claimed in claim 1, characterized in that: In the step 4), the ratio of the second suspension processing time to the first suspension processing time is 0.1 to 0.

4.

9. A lithium iron phosphate battery capacity division method as claimed in claim 3, characterized in that: In the step 5), the ratio of the third current magnification to the second current magnification is 0.05-1.

10. A lithium iron phosphate battery pack, characterized in that: The lithium iron phosphate battery pack is obtained by classifying and combining a plurality of lithium iron phosphate batteries by the method as described in any one of claims 1 to 9.

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