Battery capacity grading method and battery capacity grading system

Abstract

The application discloses a battery capacity grading method and a battery capacity grading system. The battery capacity grading method comprises the following steps: at least one pretreatment and at least one capacity grading treatment; wherein the pretreatment comprises the following steps: once charging treatment and once discharging treatment of the to-be-treated battery cell at a pretreatment rate, the charging treatment time and the discharging treatment time are the same; and the temperature of the battery cell after the at least one pretreatment is 40-55 DEG C. According to the battery capacity grading method, the temperature of the battery cell is 40-55 DEG C after the at least one pretreatment before the capacity grading treatment, the internal balance and stability of the battery cell are achieved by improving the internal temperature of the battery cell, the capacity recovery phenomenon of the battery cell is weakened, the temperature consistency of the battery cell before the capacity grading treatment is improved, the capacity consistency of the battery cell during the capacity grading treatment and the accuracy of the capacity grading treatment are improved, the reliability of the capacity grading treatment result is higher, and the battery cell grouping is indicated according to the capacity grading treatment result.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a battery capacity testing method and system. Background Technology

[0002] With batteries widely used in mobile phones, digital cameras, power tools, electric vehicles, and other fields, people are increasingly demanding higher performance from batteries, including lifespan and safety. Capacity consistency is one of the most important indicators affecting battery life. Therefore, capacity grading is an indispensable and crucial process in battery production. The typical steps for capacity grading are: first, charging (fully charging), then discharging to a specified voltage, with the discharged capacity designated as the battery's initial capacity; or first, discharging, followed by a full charge and discharge cycle, with the fully discharged capacity designated as the initial capacity. However, the accuracy of current capacity grading methods is difficult to guarantee, and cells can still experience a certain degree of capacity increase during use, resulting in relatively low reliability of the grading results. Summary of the Invention

[0003] This invention aims to at least solve one of the technical problems existing in the prior art. Therefore, one objective of this invention is to propose a battery capacity grading method that improves the capacity consistency and accuracy of cell grading, resulting in high reliability of the grading results and facilitating cell grouping based on the grading results.

[0004] According to an embodiment of the present invention, a battery capacity grading method includes the following steps: at least one pretreatment; at least one capacity grading process; wherein the pretreatment includes the following steps: performing a charging process and a discharging process on the cell to be processed at a pretreatment rate, wherein the charging process time and the discharging process time are the same; and the temperature of the cell after at least one pretreatment is 40°C to 55°C.

[0005] According to the battery capacity grading method of the present invention, at least one pretreatment is performed before the capacity grading process to make the temperature of the battery cell 40°C to 55°C. By increasing the internal temperature of the battery cell, the internal balance and stability of the battery cell are achieved, the phenomenon of capacity rebound is weakened, and the temperature consistency of the battery cell before the capacity grading process is improved. This is beneficial to improving the capacity consistency and accuracy of the capacity grading process, and the reliability of the capacity grading results is high. It is also beneficial to indicate the battery cell grouping based on the results of the capacity grading process.

[0006] According to some embodiments of the present invention, the temperature of the battery cell after at least one pretreatment is 45°C to 50°C.

[0007] According to some embodiments of the present invention, the state of charge of the battery cell to be processed is determined before the preprocessing.

[0008] According to some embodiments of the present invention, if the state of charge of the battery cell to be processed is determined to be greater than 60%, the preprocessing is to first perform the discharge processing and then the charging processing; if the state of charge of the battery cell to be processed is determined to be less than 30%, the preprocessing is to first perform the charging processing and then the discharge processing.

[0009] According to some embodiments of the present invention, the pretreatment rate is A, the capacity grading process is performed at the capacity grading rate B, and the battery has a maximum charge / discharge rate C, wherein A satisfies: B≤A<C.

[0010] According to some embodiments of the present invention, the temperature difference between any two cells that have undergone at least one of the pretreatments is less than or equal to 10°C.

[0011] According to some embodiments of the present invention, multiple capacities are measured after multiple capacity separation processes, and the capacity range of the multiple capacities is less than or equal to 8Ah.

[0012] According to some embodiments of the present invention, in multiple capacity grading processes, the highest capacity of the battery cell is α, and the lowest capacity of the battery cell is β, wherein α and β satisfy: (α-β) / β≤1%.

[0013] The battery capacity testing system according to a second aspect of the present invention employs the battery capacity testing method according to the first aspect of the present invention.

[0014] According to some embodiments of the present invention, the battery capacity testing system includes: a capacity testing workshop, wherein multiple battery cells are arranged in the capacity testing workshop for capacity testing; the temperature difference in the capacity testing workshop is less than or equal to 5°C.

[0015] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Detailed Implementation

[0016] In related technologies, the inaccurate capacity rating of batteries leads to poor battery consistency after sequential capacity matching. The specific reasons are as follows:

[0017] 1. Uneven temperature difference in the capacity testing workshop. Although the temperature difference in the capacity testing workshop is generally required to be within 5℃, due to the large area and height of the workshop (up to 15m or more), and the fact that the cells are generally stored in trays, it is not conducive to temperature uniformity among the cells. Therefore, the temperature difference in most capacity testing workshops is as high as 8℃ or more. In order to balance the temperature of the cells during capacity testing, some capacity testing workshops often use water cooling solutions. However, the equipment cost is high, the maintenance cost is high, and the reliability is low.

[0018] 2. Electrolyte wetting within the electrodes. Due to the viscosity of the electrolyte, both the positive and negative electrodes contain numerous micropores and nanopores. These nanopores gradually enlarge during charge and discharge, resulting in slow electrolyte wetting. Even after capacity testing, some pores may remain unwetted. Consequently, the cell capacity tends to increase with each charge-discharge cycle during subsequent use. In recent years, with the increasing energy density requirements of energy storage and new energy vehicles, the compaction density of the positive and negative electrodes has risen, further increasing the difficulty of electrolyte wetting. For example, batteries with higher compaction densities require more than 50 cycles to reach their maximum capacity. Therefore, it is difficult to accurately determine the battery capacity using only a single charge-discharge cycle. For example, the particle size of the lithium iron phosphate cathode material in lithium iron phosphate batteries is all at the nanoscale. Under high voltage (2.6C), there are many nanoscale pores in the cathode sheet, making it difficult for the electrolyte to wet. After capacity grading, room temperature cycling tests showed that it takes nearly 60 cycles at room temperature to reach the highest discharge capacity.

[0019] 3. Battery temperature sensitivity. Some batteries are quite sensitive to temperature, such as lithium iron phosphate batteries. Their charge and discharge capacity is significantly affected by temperature; the capacity difference can be as high as 5% or more when charging and discharging from 25℃ to 35℃. Although some temperature compensation is implemented, a significant difference still exists.

[0020] In summary, this application provides a battery capacity assessment method, and the battery capacity assessment method of the first aspect of the present invention is described below.

[0021] According to a first aspect of the present invention, a battery capacity grading method includes the following steps: at least one pretreatment and at least one capacity grading process. The pretreatment includes the following steps: subjecting the battery cell to be processed to one charging process and one discharging process at a pretreatment rate, wherein the charging process time and the discharging process time are the same; and the temperature of the battery cell after at least one pretreatment is 40°C to 55°C. Exemplarily, the temperature of the battery cell after at least one pretreatment can be any value or a range of any combination of 40°C, 43°C, 46°C, 49°C, 52°C, and 55°C.

[0022] Specifically, the battery cells undergo at least one pretreatment, namely at least one charging and one discharging process. At the pretreatment rate, heat is generated through the cell's internal resistance and polarization, raising the cell temperature to 40℃–55℃. This achieves uniform self-heating of the cell, reducing temperature differences between multiple cells and minimizing the temperature variation within the same capacity grading workshop. The pretreatment ensures sufficient contact between the cell's electrode materials and electrolyte, fully activating the cell's internal chemical activity, establishing ion transport channels, reducing capacity rebound, and improving the consistency of battery capacity grading.

[0023] When the cell temperature reaches the range of 40℃ to 55℃, the viscosity of the electrolyte can be effectively reduced, accelerating electrolyte wetting. During the pretreatment charging and discharging processes up to this temperature range, the expansion and contraction of the positive and negative electrode plates of the cell can release the internal tension of the positive and negative electrode plates, which is conducive to accelerating electrolyte diffusion and further accelerating the internal balance and stability of the cell, thus helping to improve the accuracy of capacity grading. At the same time, when the cell reaches the above temperature range, it also further promotes the stability of the negative electrode SEI (Solid Electrolyte Interphase) film and the positive electrode CEI (Cathode Electrolyte Interphase) film. Therefore, the capacity grading data can accurately reflect the actual effective capacity of the battery, providing a reliable basis for subsequent module matching, avoiding module performance degradation caused by matching deviations, and also helping to extend battery cycle life and ensure the continuity of battery performance after capacity grading.

[0024] In each pretreatment step, the charging and discharging processes are performed for the same amount of time. This ensures that the state of charge of the cells remains consistent with their initial state after pretreatment, preserving the consistency before capacity grading and minimizing the impact on the accuracy of capacity grading. The subsequent capacity grading process involves screening, classifying, and grouping the cells to improve cell consistency, extend battery cycle life, and ensure safe use.

[0025] According to the battery capacity grading method of the present invention, at least one pretreatment is performed before the capacity grading process to make the temperature of the battery cell 40°C to 55°C. By increasing the internal temperature of the battery cell, the internal balance and stability of the battery cell are achieved, the phenomenon of capacity rebound is weakened, and the temperature consistency of the battery cell before the capacity grading process is improved. This is beneficial to improving the capacity consistency and accuracy of the capacity grading process, and the reliability of the capacity grading results is high. It is also beneficial to indicate the battery cell grouping based on the results of the capacity grading process.

[0026] According to some embodiments of the present invention, the temperature of the battery cell after at least one pretreatment is 45°C to 50°C. Exemplarily, the temperature of the battery cell after at least one pretreatment can be any value or a range of any combination of 45°C, 46°C, 47°C, 48°C, 49°C, and 50°C. The battery cell undergoing at least one pretreatment raises its temperature to 45°C to 50°C, which helps to further reduce the temperature difference between cells, further improves the complete wetting of the electrolyte on the positive and negative electrode plates of the cell, and promotes the formation of a more complete negative SEI film and positive CEI film, thereby improving the consistency of the battery's capacity. Simultaneously, the increased cell temperature further increases the ambient temperature of the capacity grading workshop, while reducing the ambient temperature difference in the capacity grading workshop. The reduction in the ambient temperature difference in the capacity grading workshop further affects the temperature difference between the cells, creating a positive feedback loop.

[0027] According to some embodiments of the present invention, the state of charge (SOC) of the cell to be processed is determined before pretreatment. Before the battery capacity grading pretreatment step, determining the SOC of the cell to be processed helps to avoid damage to the electrode structure of the cell, prevents excessive ion insertion / extraction from the electrodes leading to interface film damage, ensures stable formation of the negative electrode SEI film / positive electrode CEI film during capacity grading, reduces capacity deviation, and improves the battery's capacity retention rate over multiple cycles.

[0028] According to some embodiments of the present invention, if the state of charge (SOC) of the battery cell to be processed is determined to be greater than 60%, the preprocessing involves discharging first and then charging; if the SOC of the battery cell to be processed is determined to be less than 30%, the preprocessing involves charging first and then discharging. When the SOC of the battery cell to be processed is determined to be greater than 60%, the residual charge of the battery cell may fluctuate significantly. Discharging first can remove trace amounts of gas inside the battery cell, which helps to avoid triggering overcharge protection and gas bulging, reduces polarization during subsequent charging, and activates the electrode interface, eliminating interference from residual charge and preventing CEI film decomposition due to voltage surge. When the SOC of the battery cell to be processed is determined to be less than 30%, charging first can avoid over-discharging of low-charge battery cells, effectively protect the integrity of the SEI film structure on the electrode surface, ensure stable charging and discharging efficiency of the battery cell, help the battery cell build a stable interface from a safe potential, extend its cycle life, and avoid irreversible performance damage to the battery cell.

[0029] According to some embodiments of this patent, the pretreatment rate is A, the capacity grading is performed at a grading rate B, and the battery has a maximum charge / discharge rate C, where A satisfies: B ≤ A < C. Due to the presence of internal AC resistance and polarization within the battery, at higher pretreatment rates, the AC resistance generates tab heat, which is proportional to the square of the current. As the current increases, the amount of heat generated increases exponentially. Simultaneously, at higher pretreatment rates, the internal polarization of the cell increases, generating a large amount of polarization heat. This polarization heat and Joule heat ensure that every position on the positive and negative electrodes within the cell is heated uniformly, resulting in faster and more uniform heating.

[0030] During battery capacity grading, a pretreatment rate greater than or equal to the grading rate can quickly eliminate unstable interfaces formed during cell production and storage, resulting in a more uniform ion insertion / extraction state within the cell. This also shortens pretreatment charge / discharge time, reducing processing time and meeting the efficiency requirements of mass production lines. The battery's maximum charge / discharge rate is the safety threshold for long-term stable operation. When the pretreatment rate exceeds this maximum, it leads to a sharp increase in internal polarization, causing problems such as SEI film rupture, affecting the cell's cycle life and safety performance. Therefore, during battery capacity grading, the pretreatment rate must be less than the battery's maximum charge / discharge rate to ensure cycle stability and lifespan.

[0031] According to some embodiments of the present invention, the temperature difference between any two cells that have undergone at least one pretreatment is less than or equal to 10°C. This results in a smaller temperature difference between the cells, ensuring temperature consistency among multiple cells during capacity testing, reducing the impact of temperature variables on the capacity testing process, making the capacity testing results more realistic and reliable, avoiding misjudgments of the actual cell capacity, and improving the accuracy of the capacity testing results.

[0032] According to some embodiments of the present invention, multiple capacities are measured after multiple capacity grading processes, and the capacity range of these multiple capacities is less than or equal to 8 Ah. That is, the difference between the maximum and minimum capacities among the multiple capacities of the cells is less than or equal to 8 Ah. The actual capacity of the cells is closer to the design value. During sorting, the capacity of cells in the same batch is more concentrated, allowing for rapid screening of cell combinations that meet the grouping requirements. This reduces waste of unqualified cells due to excessive tolerance and improves the accuracy of cell sorting and grouping. Consequently, the cell production process is controllable, cell performance is highly consistent, and subsequent cycle decay is more uniform. This improves the consistency of charge and discharge depths of multiple cells after grouping, preventing some cells from being in a deep cycle state for extended periods, effectively slowing down the cell aging rate, and significantly improving the overall cycle life of the battery pack. Simultaneously, the small capacity range reduces the risk of overcharging and over-discharging during battery charging and discharging, reducing safety hazards such as abnormal polarization, lithium plating, and thermal runaway caused by cell capacity imbalance, and improving the safety and stability of the battery.

[0033] According to some embodiments of the present invention, in multiple capacity grading processes, the highest capacity of the battery cell is α, and the lowest capacity of the battery cell is β, wherein α and β satisfy: (α-β) / β≤1%. For example, (α-β) / β can be any value from 0.1%, 0.3%, 0.5%, 0.7%, 0.9%, 1%, or a range of any combination of both. In multiple capacity grading processes, the highest and lowest capacities of the battery cell are measured, and the ratio of the difference between the highest and lowest capacities to the lowest value is less than or equal to 1%. That is, the capacity of the battery cell does not change significantly during multiple capacity grading processes. Therefore, this ensures the authenticity of the capacity grading data, improves the accuracy of cell grouping, prevents fluctuations in the capacity of each cell due to subsequent recovery, improves the consistency of battery capacity after grouping, avoids voltage imbalance and polarization accumulation between cells, helps improve the cycle stability of the battery, and extends the cycle life of the battery. Therefore, the battery can complete charge-discharge cycles within a range close to its theoretical total capacity, which can maximize the actual usable capacity of the battery pack, improve energy utilization, and at the same time facilitate the synchronization of cell charge-discharge depth, thus extending the cycle life of the battery pack.

[0034] The battery capacity testing system according to a second aspect of the present invention employs the battery capacity testing method according to the first aspect of the present invention.

[0035] According to the battery capacity grading system of the present invention, since the battery capacity grading system adopts the above-mentioned battery capacity grading method, the accuracy of capacity calibration is improved, thereby helping to improve the consistency and stability of the battery, and also helping to shorten the capacity grading process and improve the production line efficiency.

[0036] According to some embodiments of the present invention, a battery capacity testing system includes a capacity testing workshop, which is suitable for arranging multiple battery cells for capacity testing; the temperature difference within the capacity testing workshop is less than or equal to 5°C. For example, the temperature difference within the capacity testing workshop can be any value from 1°C, 2°C, 3°C, 4°C, and 5°C, or a range of any combination of both. Multiple battery cells can be tested simultaneously within the capacity testing workshop, improving the utilization rate of equipment and space within the workshop and avoiding energy consumption fluctuations caused by frequent equipment start-ups and shutdowns. Simultaneously, the simultaneous testing of multiple battery cells maximizes the use of a relatively uniform temperature environment, ensuring consistent testing conditions for the cells under test, which is more conducive to subsequent battery grouping and quality control. Controlling the temperature difference within the capacity testing workshop within the aforementioned range avoids localized high or low temperatures, ensuring that the electrochemical reactions of the cells under test occur under relatively identical conditions, making the measured cell capacity closer to the true value and reducing misjudgments caused by uneven ambient temperature. Meanwhile, within the aforementioned capacity testing workshop, the probability of heat generation and dissipation of the batteries remains synchronized, avoiding localized high-temperature areas, reducing environmental interference, and improving the consistency of cells from the same batch.

[0037] In summary, the capacity grading method of this application performs at least one pretreatment before the grading process. By charging and discharging for the same duration at the pretreatment rate, the cell's internal polarization is achieved, resulting in more uniform self-heating within the cell. This accelerates electrolyte wetting, which helps improve the consistency of battery capacity grading and reduces the phenomenon of cell capacity rebound. Simultaneously, the cell's self-heating also helps raise the temperature within the capacity grading workshop, avoiding localized high-temperature areas and improving the accuracy and reliability of the battery capacity grading system.

[0038] The embodiments of the present invention are described in detail below. It should be noted that the embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. In addition, unless otherwise specified, all reagents used in the following embodiments are commercially available or can be synthesized according to the methods described herein or known to others. For reaction conditions not listed, they are also readily available to those skilled in the art.

[0039] Example 1

[0040] The battery in Example 1 is a square aluminum-cased battery with a rated capacity of 314 Ah. During the formation process, the charge is 75% of the rated capacity. The positive electrode active material is lithium iron phosphate, and the negative electrode active material is artificial graphite. The organic electrolyte includes: organic solvents (dimethyl carbonate, ethyl methyl carbonate, and ethylene carbonate), lithium salts (with added lithium hexafluorophosphate and lithium difluorosulfonylimide), and film-forming agents (ethylene carbonate, ethylene sulfate, fluoroethylene carbonate, and tris(trimethylsilyl)phosphate).

[0041] The battery in this embodiment is subjected to the following capacity grading method:

[0042] (1) Place the battery in the capacity testing room and let it stand for 1 minute. The initial temperature of the capacity testing room is 30°C.

[0043] (2) Discharge multiple cells in the battery with constant current (471A) for 20 minutes. According to the formula: current (I) = rate (C) × battery rated capacity (Ah), the pretreatment rate is 1.5C.

[0044] (3) Let the multiple cells processed in step (2) stand for 1 minute;

[0045] (4) After the multiple cells processed in step (3) are charged at a constant current (471A) for 20 minutes and left to stand for 1 minute, the surface temperature of the cells is measured to be 46℃~49℃.

[0046] (5) Perform multiple capacity tests on the cells after step (4) and measure multiple capacities. See Table 1 for specific parameters.

[0047] Table 1. Capacity partitioning method of Example 1

[0048]

[0049] Example 2

[0050] The battery in Example 2 is a square aluminum-cased battery with a rated capacity of 314 Ah. During the formation process, the charge is 30% of the rated capacity. The positive electrode active material is lithium iron phosphate, and the negative electrode active material is artificial graphite. The organic electrolyte includes: organic solvents (dimethyl carbonate, ethyl methyl carbonate, and ethylene carbonate), lithium salts (with added lithium hexafluorophosphate and lithium difluorosulfonylimide), and film-forming agents (ethylene carbonate, ethylene sulfate, fluoroethylene carbonate, and tris(trimethylsilyl)phosphate).

[0051] The battery in this embodiment is subjected to the following capacity grading method:

[0052] (1) Place the battery in the capacity testing room and let it stand for 1 minute. The initial temperature of the capacity testing room is 23°C.

[0053] (2) Charge multiple cells in the battery with constant current (471A) for 25 minutes. According to the formula: current (I) = rate (C) × battery rated capacity (Ah), the pretreatment rate is 1.5C.

[0054] (3) Let the multiple cells processed in step (2) stand for 1 minute;

[0055] (4) Discharge multiple cells processed in step (3) at a constant current (471A) for 25 minutes, let them stand for 1 minute, and measure the surface temperature of the cells to be 45℃~48℃.

[0056] (5) Perform multiple capacity tests on the cells after step (4) and measure multiple capacities. See Table 2 for specific parameters.

[0057] Table 2. Capacity partitioning method in Example 2

[0058]

[0059] Example 3

[0060] The battery in Example 3 is a square aluminum-cased battery with a rated capacity of 30Ah. During the formation process, the charge is 65% of the rated capacity. The positive electrode active material is lithium iron phosphate, the negative electrode active material is artificial graphite, and the organic electrolyte includes: organic solvents (dimethyl carbonate, ethyl methyl carbonate, and ethylene carbonate), lithium salt (lithium hexafluorophosphate), and film-forming agents (ethylene carbonate and fluoroethylene carbonate).

[0061] The battery in this embodiment is subjected to the following capacity grading method:

[0062] (1) Place the battery in the capacity testing room and let it stand for 1 minute. The initial temperature of the capacity testing room is 26°C.

[0063] (2) Discharge multiple cells in the battery with constant current (60A) for 15 minutes. According to the formula: current (I) = rate (C) × battery rated capacity (Ah), the pretreatment rate is 2C.

[0064] (3) Let the multiple cells processed in step (2) stand for 1 minute;

[0065] (4) After the multiple cells processed in step (3) are charged at a constant current (60A) for 15 minutes and left to stand for 1 minute, the surface temperature of the cells is measured to be 47℃~49℃.

[0066] (5) Perform multiple capacity tests on the cells after step (4) and measure multiple capacities. See Table 3 for specific parameters.

[0067] Table 3. Capacity separation method in Example 3

[0068]

[0069] Comparative Example 1

[0070] This comparative example is basically the same as Example 1, except that: no pretreatment is performed, the battery is placed in the capacity testing room and left to stand for 1 minute before the capacity testing is performed. The capacity testing method is the same as that in Example 1, and the specific parameters are shown in Table 4.

[0071] Table 4. Capacity division method for Comparative Example 1

[0072]

[0073] Comparative Example 2

[0074] This comparative example is basically the same as Example 2, except that: no pretreatment is performed, the battery is placed in the capacity testing room and left to stand for 1 minute before the capacity testing is performed. The capacity testing method is the same as that in Example 2, and the specific parameters are shown in Table 5.

[0075] Table 5. Capacity division method for Comparative Example 2

[0076]

[0077] Comparative Example 3

[0078] This comparative example is basically the same as Example 3, except that no pretreatment is performed. The battery is placed in the capacity testing room and left to stand for 1 minute before the capacity testing is performed. The capacity testing method is the same as that in Example 3. The specific parameters are shown in Table 6.

[0079] Table 6. Capacity partitioning method for Comparative Example 3

[0080]

[0081] Performance testing methods

[0082] (1) Cell temperature test

[0083] Each cell in the capacity testing cabinet is equipped with a cell surface temperature sensor at the capacity testing point, and the temperature detected by the temperature sensor is the cell temperature.

[0084] (2) Temperature test in the capacity testing workshop

[0085] Each storage location in the capacity distribution cabinet will have more than one temperature sensor, and the temperature detected by this temperature sensor will be the temperature of the capacity distribution workshop.

[0086] (3) Cell cycle test

[0087] After the cells have been divided into different capacities, they are left to rest for 12 hours, then placed in a constant temperature chamber at 25±2℃ for another 12 hours. Then, charge and discharge cycle tests are performed. The charge and discharge rate, cut-off voltage, and current are tested in a charge-discharge cycle mode of charging first and then discharging. The capacity of the second discharge is recorded as the initial capacity of the cell. The number of cycles and the maximum capacity of the cycle are tested. The tolerance is obtained by subtracting the maximum capacity of the cycle from the initial capacity of the cell.

[0088] The performance test results are shown in Table 7.

[0089] Table 7 Performance test results of the examples and comparative examples

[0090]

[0091] Test Result Analysis

[0092] A comparison of Examples 1-3 and Comparative Examples 1-3 shows that performing at least one pretreatment before capacity testing reduces the temperature difference in the capacity testing workshop and the temperature difference between cells, which helps to reduce the impact of temperature variables on capacity testing and improve the accuracy of capacity testing results.

[0093] In this embodiment, the number of charge-discharge cycles required for the battery cell to reach its maximum capacity is lower than that of the corresponding comparative embodiment. This fully preserves the effective capacity of the battery, which is beneficial for improving the cycle life and charge-discharge efficiency stability of the battery cell, increasing the efficiency of the production line turnover, and reducing the loss of energy equipment.

[0094] During the multiple capacity testing processes, the cell tolerance of Examples 1-3 is less than 1%, which is much lower than that of Comparative Examples 1-3. This is beneficial for improving the capacity consistency of the batteries after grouping and extending the cycle life of the battery pack.

[0095] Furthermore, the results of the cell cycle test show that the pre-treated cells in Examples 1-3 can reach the maximum cell cycle capacity more quickly with fewer cycles, which helps to reduce the cell cycle tolerance (i.e., the difference between the maximum cell cycle capacity and the initial cell capacity), thus extending the cell's service life and improving its safety.

[0096] Other configurations and operations of the battery capacity testing method and battery capacity testing system according to embodiments of the present invention are known to those skilled in the art and will not be described in detail here.

[0097] In the description of this specification, references to terms such as "some embodiments" indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example.

[0098] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A battery capacity testing method, characterized in that, Includes the following steps: At least one preprocessing step; At least one capacity splitting process; The pretreatment includes the following steps: the battery cell to be treated is charged once and discharged once at the pretreatment rate, and the charging time is the same as the discharging time. And after at least one pretreatment, the temperature of the battery cell is 40℃~55℃; Before the preprocessing, the state of charge of the battery cell to be processed is determined, and the state of charge of the battery cell to be processed is used to determine whether to perform charging or discharging processing first.

2. The battery capacity assessment method according to claim 1, characterized in that, After at least one pretreatment, the temperature of the battery cell is 45°C to 50°C.

3. The battery capacity testing method according to claim 1, characterized in that, If the state of charge of the battery cell to be processed is determined to be greater than 60%, the preprocessing is to first perform the discharge process and then the charging process. If the state of charge of the battery cell to be processed is determined to be less than 30%, the preprocessing is to first perform the charging process and then the discharging process.

4. The battery capacity testing method according to claim 1, characterized in that, The pretreatment rate is A, the capacity grading process is performed at the capacity grading rate B, and the battery has a maximum charge / discharge rate C, wherein A satisfies: B≤A<C.

5. The battery capacity testing method according to any one of claims 1-4, characterized in that, The temperature difference between any two cells that have undergone at least one of the pretreatments is less than or equal to 10°C.

6. The battery capacity testing method according to any one of claims 1-4, characterized in that, After multiple capacity separation processes, multiple capacities were measured, and the capacity range of the multiple capacities was less than or equal to 8 Ah.

7. The battery capacity testing method according to any one of claims 1-4, characterized in that, In the multiple capacity grading processes, the highest capacity of the battery cell is α, and the lowest capacity of the battery cell is β, wherein α and β satisfy: (α-β) / β≤1%.

8. A battery capacity grading system, characterized in that, The battery capacity testing method according to any one of claims 1-7 is adopted.

9. The battery capacity grading system according to claim 8, characterized in that, include: Capacity testing workshop, wherein multiple battery cells are arranged for capacity testing; The temperature difference within the capacity-dividing workshop is less than or equal to 5°C.

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