A method for sorting lithium battery capacity

Abstract

The application provides a capacity grading method for improving the capacity of a lithium battery, which comprises a charging step of charging the lithium battery at a first preset charging rate, and stopping charging when the state of charge (SOC) value of the lithium battery is within a first SOC threshold range; and a discharging step of discharging the lithium battery at a second preset discharging rate, and stopping discharging when the SOC value of the lithium battery is within a second SOC threshold range; wherein the charging step and the discharging step are executed alternately, and the charging step is executed at least twice and the discharging step is executed at least twice. The capacity grading method provided by the application can release the stress of the negative electrode material in the lithium ion deintercalation process as much as possible, expand the interlayer spacing of the negative electrode material, make the lithium ion more easily deintercalate from the negative electrode material, thereby reduce the internal resistance of the lithium ion battery, and improve the capacity of the lithium battery.

Description

Technical Field

[0001] This application relates to the field of lithium battery technology, and more specifically, to a capacity grading method for improving the capacity of lithium batteries. Background Technology

[0002] Lithium-ion batteries have been widely used in vehicles and other fields due to their advantages such as high packaging reliability, good durability, and relatively simple assembly. However, the capacity of mass-produced lithium-ion batteries may vary. To ensure the normal use of lithium-ion batteries, they need to be capacity-tested at the factory to determine their actual capacity.

[0003] During charging, some lithium ions are released from the positive electrode material (e.g., lithium iron phosphate) and transferred to the negative electrode via the electrolyte, where they are embedded in the negative electrode material (e.g., graphite). During discharging, lithium ions are released from the negative electrode material and transferred to the positive electrode via the electrolyte. However, most existing lithium-ion batteries exhibit a low initial capacity rating, leading to increased cell design costs. Summary of the Invention

[0004] This application provides a capacity grading method for improving the capacity of lithium batteries, which can reduce the internal resistance of lithium-ion batteries and increase the capacity of lithium batteries.

[0005] Specifically, this application is implemented through the following technical solution:

[0006] This application provides a capacity grading method for increasing the capacity of lithium batteries, including:

[0007] The charging process involves charging the lithium battery at a first preset charging rate, and stopping charging when the state of charge (SOC) value of the lithium battery is within the first SOC threshold range.

[0008] The discharge step involves discharging the lithium battery at a second preset discharge rate, and stopping the discharge when the state of charge (SOC) value of the lithium battery is within the second SOC threshold range.

[0009] The charging and discharging steps are performed alternately, with each step being performed at least twice. This maximizes the release of stress in the negative electrode material during lithium-ion intercalation / deintercalation, increases the interlayer spacing of the negative electrode material, and facilitates lithium-ion intercalation / deintercalation, thereby reducing the internal resistance of the lithium-ion battery and increasing its capacity.

[0010] Optionally, the first SOC threshold range is 80-100%; the second SOC threshold range is 60-99%; and the SOC value of the lithium battery at the point where charging stops is greater than the SOC value of the lithium battery at the point where discharging stops. Therefore, while increasing the lithium battery capacity, the time required to cycle through the charging and discharging steps can be shortened, reducing time costs.

[0011] Optionally, during the execution of at least two of the charging steps, the state of charge (SOC) values ​​of each of the lithium batteries at the time of stopping charging are not equal.

[0012] During at least two discharge steps, the state of charge (SOC) values ​​of each lithium battery at the point of discharge cessation are different. This facilitates more complete activation of the negative electrode material, allowing for sufficient release of stress on the negative electrode material during lithium-ion insertion / extraction.

[0013] Optionally, during the execution of at least two of the charging steps, at least one of the state of charge (SOC) values ​​of each of the lithium batteries at the time of stopping charging is equal to 100%.

[0014] During at least two of the discharge steps, at least one of the states of charge (SOC) values ​​of the respective lithium batteries at the point of discharge cessation is less than 80%. This is beneficial for reducing Li-ion battery capacity. 0.5 C6 compounds overcome the resistance to solid-phase diffusion, promoting Li 0.5 C6 compounds can complete the conversion of LiC6 compounds, which is more conducive to reducing the internal resistance of lithium batteries and increasing battery capacity.

[0015] Optionally, the number of times the charging step and the number of times the discharging step are performed do not exceed 30. This maximizes the battery capacity, bringing it closer to or even reaching the standard capacity, while also reducing the time cost of capacity grading.

[0016] Optionally, the number of times the charging step is performed and the number of times the discharging step is performed are both within the range of 5-20. This significantly reduces the probability of the cutoff voltage reaching its maximum prematurely during the discharging process, minimizing the possibility of a small capacity increase after multiple charge-discharge cycles following the capacity grading process. This greatly increases the battery capacity and reduces battery production costs.

[0017] Optionally, both the first preset charging rate range and the second preset discharging rate range are 0.5-10C. This achieves rapid charging and discharging of the battery without damaging its electrical performance.

[0018] Optionally, during the charging and discharging steps, the ambient temperature of the lithium battery is controlled within the range of 20-60°C. This provides a more suitable ambient temperature for stress release of the negative electrode material and lithium-ion diffusion, thereby improving capacity grading efficiency.

[0019] Optionally, after the charging step is completed but before the discharging step is performed, the method further includes...

[0020] The first settling step involves subjecting the lithium battery to a settling process for 1-5 minutes. This ensures that the insertion and extraction of lithium ions in the positive and negative electrode materials reach a dynamic equilibrium after the battery has finished charging.

[0021] Optionally, after performing the discharge step, the method further includes...

[0022] The second settling step involves subjecting the lithium battery to a second settling treatment, which lasts for 1-5 minutes. This ensures that the insertion and extraction of lithium ions in the positive and negative electrode materials reach a dynamic equilibrium after the battery has finished discharging.

[0023] The technical solution provided in this application can achieve the following beneficial effects:

[0024] This application provides a capacity grading method for improving the capacity of lithium batteries, which can release the stress of the negative electrode material during the lithium-ion intercalation and deintercalation process as much as possible, expand the interlayer spacing of the negative electrode material, and make it easier for lithium ions to be intercalated and deintercalated from the negative electrode material, thereby reducing the internal resistance of the lithium-ion battery and improving the capacity of the lithium battery. Attached Figure Description

[0025] Figure 1 This is a flowchart illustrating a capacity testing method for a lithium battery according to an exemplary embodiment of this application.

[0026] Figure 2 This is a flowchart illustrating another capacity testing method for lithium batteries according to an exemplary embodiment of this application.

[0027] Figure 3 This is a schematic diagram illustrating the principle of lithium ions embedding into the negative electrode material during capacity testing in a lithium battery, as shown in an exemplary embodiment of this application.

[0028] Figure 4 This is a comparison graph showing the capacity retention rate of a lithium battery after multiple charge-discharge cycles before and after the improvement of the capacity grading method, as illustrated in an exemplary embodiment of this application. Detailed Implementation

[0029] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. In the following description, when referring to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments are merely illustrative of the concept of this application and do not represent all embodiments of the concept of this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of the concept of this application.

[0030] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to limit the application. Unless otherwise defined, the technical or scientific terms used in this application should be understood in their ordinary sense by one of ordinary skill in the art to which this application pertains. The terms "first," "second," and similar terms used in this application specification and claims do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, the terms "a" or "one," etc., do not indicate a quantity limitation, but rather indicate the presence of at least one. "A plurality" or "several" indicates two or more. Unless otherwise indicated, the terms "front," "rear," "lower," and / or "upper," "top," "bottom," etc., are for ease of description only and are not limited to a location or spatial orientation. The terms "comprising" or "including," etc., mean that the elements or objects preceding "comprising" or "including" cover the elements or objects listed after "comprising" or "including" and their equivalent elements or objects, and other elements or objects are not excluded in this application. The word “connection” or “link” is not limited to physical or mechanical connections, but can also include electrical connections, whether direct or indirect.

[0031] Please see Figure 1 This application discloses a capacity grading method for improving the capacity of lithium batteries, comprising:

[0032] The charging process involves charging the lithium battery at a first preset charging rate, and stopping charging when the state of charge (SOC) value of the lithium battery is within the first SOC threshold range.

[0033] The discharge step involves discharging the lithium battery at a second preset discharge rate, and stopping the discharge when the state of charge (SOC) value of the lithium battery is within the second SOC threshold range.

[0034] The charging step and the discharging step are executed alternately in sequence, and the charging step and the discharging step are executed at least twice and at least twice respectively.

[0035] Currently, the capacity grading process for lithium-ion batteries involves fully discharging the battery once using a specific current rate (i.e., charging it once and then discharging it completely in one go). Data from each detection point is obtained through a device management system to analyze the battery's capacity and internal resistance. However, the negative electrode of lithium-ion batteries is typically made of graphite, which has a hexagonal layered structure. During the first charge of a lithium-ion battery, the negative electrode does not fully reach the LiC6 state. This is especially true for lithium iron phosphate batteries, where the negative electrode potential is high, meaning some graphite layers have very low lithium intercalation. The stress between the graphite layers is not released, resulting in high diffusion resistance and causing the charging cutoff voltage to be reached prematurely. This leads to a lower initial capacity grading and increased design costs. In this embodiment, the capacity grading process involves cyclically executing at least two charging steps and at least two discharging steps. One cycle consists of performing one charging step followed by one discharging step. This cycle is repeated, and then another charging step and a discharging step are performed sequentially to complete another cycle. By utilizing at least two charge-discharge cycles to promote the reciprocating motion of lithium ions, the stress on the negative electrode material during the lithium ion insertion / extraction process can be released as much as possible, expanding the interlayer spacing of the negative electrode material and making it easier for lithium ions to be inserted / extracted from the negative electrode material. This reduces the internal resistance of the lithium-ion battery and increases its capacity.

[0036] It's important to note that the charge / discharge rate of a battery is a measure of how fast it charges and discharges. It can be understood as follows: if a battery's rated current is 500mA, it can be fully charged in one hour using a constant current charging method at that rated current. The battery capacity is represented by C. Therefore, a charge / discharge rate of 1C means that the battery can be fully charged / discharged in one hour using a constant current of 500mA. A charge / discharge rate of 0.5C means that the battery can be fully charged / discharged in two hours using a constant current of 250mA. In other words, the charge / discharge rate represents the ratio of the actual charge / discharge current to the rated current; one charge / discharge rate corresponds to one charge / discharge current. For example, if the rated current is 500mA and the charge / discharge rate is 0.5C, then the corresponding charge / discharge current is 250mA. A charge / discharge rate of 1C corresponds to a corresponding charge / discharge current of 500mA. The state of charge (SOC) of a battery is used to characterize its remaining capacity, which can be greater than or equal to 0% and less than or equal to 100%. The SOC can be determined using technologies such as device management systems.

[0037] In one embodiment, the first SOC threshold ranges from 80% to 100%; the second SOC threshold ranges from 60% to 99%; and the SOC value of the lithium battery when charging stops is greater than the SOC value of the lithium battery when discharging stops.

[0038] In the charging step, the lithium battery is charged at a first preset charging rate. Charging stops when the state of charge (SOC) of the lithium battery is greater than or equal to 80% and less than or equal to 100%. In the discharging step, the lithium battery is discharged at a second preset discharging rate. Discharging stops when the SOC of the lithium battery is greater than or equal to 60% and less than or equal to 99%. For example, the lithium battery is charged at the first preset charging rate, and charging stops when the SOC reaches 90%. Then, the lithium battery is discharged at the second preset discharging rate, and discharging stops when the SOC decreases from 90% to 80%. Another example is charging at the first preset charging rate, and charging stops when the SOC reaches 100%. Then, the lithium battery is discharged at the second preset discharging rate, and discharging stops when the SOC decreases from 100% to 99%. Of course, this is not the only possible approach.

[0039] In this embodiment, by setting the first SOC threshold range and the second SOC threshold range to the ranges described above, the capacity of the lithium battery can be increased while the time for cyclically executing the charging and discharging steps can be shortened, thus reducing time costs.

[0040] Of course, the selection of the first SOC threshold range and the second SOC threshold range is not limited to these. In other embodiments, if time costs are not considered, the first SOC threshold range can also be greater than or equal to 1% and less than or equal to 100%, and the second SOC threshold range can also be greater than or equal to 0% and less than or equal to 99%. The requirement is that the SOC value of the lithium battery at the time of stopping charging is greater than the SOC value of the lithium battery at the time of stopping discharging.

[0041] In one embodiment, during the execution of at least two of the charging steps, the state of charge (SOC) values ​​of the respective lithium batteries at the time of stopping charging are not equal.

[0042] During the execution of at least two discharge steps, the state of charge (SOC) values ​​of each of the lithium batteries at the point of stopping discharge are not equal.

[0043] For example, in the first charging step, charging stops when the state of charge (SOC) of the lithium battery reaches 95%; in the first discharging step, discharging stops when the SOC decreases from 95% to 75%; then, in the second charging step, charging stops when the SOC reaches 97%; and in the second discharging step, discharging stops when the SOC decreases from 97% to 78%. Of course, this is not the only possible approach. Therefore, the SOC of the lithium battery at the point where charging or discharging stops is different after each charge / discharge cycle, facilitating more complete activation of the negative electrode material and allowing for sufficient release of stress during the lithium-ion intercalation / deintercalation process.

[0044] In one embodiment, during the execution of at least two of the charging steps, at least one of the state of charge (SOC) values ​​of each of the lithium batteries at the time of stopping charging is equal to 100%.

[0045] During the execution of at least two of the discharge steps, at least one of the states of charge (SOC) values ​​of the respective lithium batteries at the time of stopping the discharge is less than 80%.

[0046] like Figure 3 The diagram illustrates the principle of lithium-ion intercalation into the graphite anode material. The battery is charged at a specific charging rate, and as charging progresses, lithium ions from the cathode material gradually intercalate into the graphite anode material layer. Typically, the graphite I-phase LiC6 begins to appear when the state of charge (SOC) reaches 80%, at which point Li... 0.5 C6 compounds begin to transform into LiC6 compounds, and the relative lithium concentration of LiC6 compounds can be increased to the design value of lithium batteries until the state of charge (SOC) reaches 100%. Therefore, by controlling at least one SOC value of each lithium battery within the first SOC threshold range to equal 100%, and controlling at least one SOC value of each lithium battery within the second SOC threshold range to be less than 80%, it is beneficial to reduce Li... 0.5 C6 compounds overcome the resistance to solid-phase diffusion, promoting Li 0.5 C6 compounds can complete the conversion of LiC6 compounds, which is more conducive to reducing the internal resistance of lithium batteries and increasing battery capacity.

[0047] In one embodiment, the number of times the charging step is performed and the number of times the discharging step is performed do not exceed 30. For example, it can be 20, 25, 28, or 30 times, but it is not limited to these. This maximizes the battery capacity, bringing it closer to or even reaching the standard capacity, while also reducing the time cost of capacity grading.

[0048] In one embodiment, the number of times the charging step is performed and the number of times the discharging step is performed both range from 5 to 20. This significantly reduces the likelihood of the cutoff voltage reaching its maximum prematurely during the discharge process, minimizing the possibility of a small capacity increase after multiple charge-discharge cycles following the capacity grading process. This greatly increases battery capacity and reduces battery production costs.

[0049] Please see Figure 4 , Figure 4 The horizontal axis represents the number of charge-discharge cycles, and the vertical axis represents the capacity retention rate. The lithium battery is improved using the capacity grading method described in this application. The lithium battery is charged at 0.5C, and charging is stopped when the State of Charge (SOC) reaches 100%. Then, it is discharged at 0.5C, and discharging is stopped when the SOC reaches 80%. This cycle is repeated 20 times. The initial capacity retention rate of the tested lithium battery after capacity grading is 100%, and no capacity increase is observed after multiple charge-discharge cycles. In contrast, the capacity grading method using a single charge-discharge cycle (i.e., one full discharge) results in a 95% initial capacity retention rate. After multiple charge-discharge cycles, a capacity increase occurs; the capacity retention rate only reaches 100% after approximately 110 cycles. Before this, the actual capacity of the lithium battery does not reach the standard capacity. It can be seen that, with the capacity grading method provided in this application, the initial capacity after capacity grading can reach the standard capacity, which greatly improves the capacity of lithium batteries and saves the design cost of lithium battery materials.

[0050] In one embodiment, the range of both the first preset charging rate and the second preset discharging rate is 0.5-10C. This allows for rapid charging and discharging of the battery without damaging its electrical performance.

[0051] In one embodiment, during the charging and discharging steps, the ambient temperature of the lithium battery is controlled within the range of 20-60°C. This provides a more suitable ambient temperature for stress release of the negative electrode material and lithium-ion diffusion, thereby improving capacity grading efficiency.

[0052] Please see Figure 2 In one embodiment, after the charging step is completed and before the discharging step is performed, the method further includes...

[0053] The first settling step involves subjecting the lithium battery to a settling process for 1-5 minutes. This ensures that the insertion and extraction of lithium ions in the positive and negative electrode materials reach a dynamic equilibrium after the battery has finished charging.

[0054] In one embodiment, after performing the discharge step, the method further includes...

[0055] The second settling step involves subjecting the lithium battery to a second settling treatment, which lasts for 1-5 minutes. This ensures that the insertion and extraction of lithium ions in the positive and negative electrode materials reach a dynamic equilibrium after the battery has finished discharging.

[0056] It should be noted that the batteries mentioned in this article can be one or more batteries or one or more battery cells. They can use either solid-state electrolytes for lithium-ion transport or the separators and electrolytes found in traditional batteries.

[0057] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A capacity grading method for improving the capacity of lithium batteries, characterized in that, include: The charging process involves charging the lithium battery at a first preset charging rate, and stopping charging when the state of charge (SOC) of the lithium battery is greater than or equal to 80% and less than or equal to 100%. The discharge step involves discharging the lithium battery at a second preset discharge rate. Discharging is stopped when the state of charge (SOC) of the lithium battery is greater than or equal to 60% and less than or equal to 99%. The charging and discharging steps are performed alternately, with each step being performed at least twice. The state of charge (SOC) of the lithium battery at the point where charging stops is greater than the SOC of the lithium battery at the point where discharging stops. During the execution of at least two charging steps, the SOC values ​​of the individual lithium batteries at the point where charging stops are unequal. Similarly, during the execution of at least two discharging steps, the SOC values ​​of the individual lithium batteries at the point where discharging stops are unequal.

2. The capacity grading method for increasing lithium battery capacity according to claim 1, characterized in that: During the execution of at least two of the charging steps, at least one of the states of charge (SOC) values ​​of each of the lithium batteries at the time of stopping charging is equal to 100%; During the execution of at least two of the discharge steps, at least one of the states of charge (SOC) values ​​of the respective lithium batteries at the time of stopping the discharge is less than 80%.

3. The capacity grading method for increasing lithium battery capacity according to claim 1 or 2, characterized in that: The number of times the charging step is performed and the number of times the discharging step is performed do not exceed 30.

4. The capacity grading method for increasing lithium battery capacity according to claim 1 or 2, characterized in that: The number of times the charging step is performed and the number of times the discharging step is performed are both in the range of 5-20.

5. The capacity grading method for increasing lithium battery capacity according to claim 1 or 2, characterized in that: The range of the first preset charging rate and the range of the second preset discharging rate are both 0.5-10C.

6. The capacity grading method for increasing lithium battery capacity according to claim 1 or 2, characterized in that: During the charging and discharging processes, the ambient temperature of the lithium battery is controlled to be between 20-60°C.

7. The capacity grading method for increasing lithium battery capacity according to claim 1 or 2, characterized in that: After the charging step is completed and before the discharging step is performed, the process also includes... The first settling step involves subjecting the lithium battery to a first settling treatment; the first settling treatment time is 1-5 minutes.

8. The capacity grading method for increasing lithium battery capacity according to claim 1 or 2, characterized in that: After performing the discharge step, the process also includes... The second settling step involves subjecting the lithium battery to a second settling process; the settling time is 1-5 minutes.

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