Battery capacity grading method

Abstract

This invention discloses a battery capacity rating method, comprising the following steps: obtaining the first discharge capacity and the second total discharge capacity of multiple groups of capacity-rated batteries during their first factory discharge; constructing a relationship model between the first discharge capacity and the second total discharge capacity, based on which the second total discharge capacity can be obtained from the first factory discharge of the batteries; performing the first factory discharge of unrated batteries to obtain their discharge capacity, and obtaining the total discharge capacity of the unrated batteries based on the relationship model; and charging and adjusting the load of the unrated batteries to obtain the unrated battery capacity. SOC Voltage. The beneficial effects of this invention are: by studying the first discharge capacity and the second total discharge capacity of multiple groups of pre-sized batteries during their initial factory discharge, a relationship model between the first discharge capacity and the second total discharge capacity is constructed. This means that after obtaining the discharge capacity of unsized batteries during their first factory discharge, the total discharge capacity of unsized batteries can be obtained, thus directly omitting the full charge and full discharge steps.

Description

Technical Field

[0001] This invention relates to the field of battery manufacturing technology, and more particularly to a battery capacity testing method. Background Technology

[0002] Capacity testing is an essential and crucial step in the production of lithium-ion batteries. Through this process, the capacity of each cell can be measured, and defective cells can be eliminated to ensure that the battery's performance and capacity meet requirements, thereby improving the quality of battery modules and batteries. Pack The consistency, reliability, and performance stability of the battery pack are improved, reducing the impact of the "weakest link" effect. Currently, most battery manufacturers use the ampere-hour integration method to measure the capacity of the battery cells: it calculates the battery capacity based on the accumulation of current and the integration of time during the charging and discharging process, and is generally divided into three main steps: full charge, full discharge, and load adjustment.

[0003] The publication number is CN 111697271 A A Chinese patent document discloses a method for forming and capacity testing lithium-ion batteries, comprising the following steps: 1. After assembling and filling with electrolyte, the battery is left to stand; 2. Primary formation; 3. After standing the battery cells treated in step 2, capacity testing is performed; 4. The battery is left to stand and the results are recorded; 5. Constant current and constant voltage charging is performed, with a cutoff current of 0.05V. C Charge to 100% SOC Record this charging capacity as Q 2. Perform discharge adjustment again. SOC 6. After testing, the batteries are taken offline, sorted, and stored in the warehouse, completing the lithium-ion battery formation and capacity testing. This is achieved by employing a new lithium-ion battery formation and capacity testing method, using two self-discharge testing methods: one for capacity characterization and the other for other applications. k The method of characterization is used to ensure that cells with poor self-discharge are screened out, thereby more accurately reflecting the self-discharge status of the battery.

[0004] See Figure 5 and Figure 6 In fact, the commonly used capacity testing method generally consists of three steps: full charge step: charging to the upper limit cutoff voltage; full discharge step: discharging to the lower limit cutoff voltage; and load adjustment step: charging to the level required for self-discharge testing. SOC Status. This method can accurately measure the true capacity of each battery with good precision and accuracy, but it also has the following disadvantages: First, the process time is long, ranging from 4 to 5 days. h First, production efficiency is low; second, in order to meet the production cycle, a large number of capacity testing equipment needs to be purchased, resulting in large equipment investment and a large factory area; third, the energy consumption is high for the complete charging and discharging of the battery cells.

[0005] The information disclosed in this background section is intended only to enhance the understanding of the overall background of the invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0006] The technical problem to be solved by this invention is the low battery capacity utilization efficiency.

[0007] The present invention solves the above-mentioned technical problems through the following technical means:

[0008] This invention claims protection for a battery capacity grading method, comprising the following steps: Obtain the first discharge capacity and the second total discharge capacity of multiple groups of pre-sized batteries during their first discharge at the factory; A model relating the first discharge capacity to the second total discharge capacity is constructed. Based on this model, the second total discharge capacity can be obtained from the battery's first discharge at the factory. For the first discharge of un-rated batteries, obtain the discharge capacity of the un-rated batteries, and based on the relationship model, obtain the total discharge capacity of the un-rated batteries; Charge and adjust the load of un-capacitated batteries to obtain un-capacitated batteries. SOC Voltage; Complete the capacity testing of untested batteries.

[0009] By studying the first discharge capacity and the second total discharge capacity after full discharge of multiple groups of pre-sized batteries, a relationship model between the first discharge capacity and the second total discharge capacity is constructed. This means that after obtaining the discharge capacity of unsized batteries from their first discharge, the total discharge capacity of unsized batteries can be obtained, thus directly omitting the full charge and full discharge steps, due to the load adjustment step... SOC The range is relatively low, only 5%-20% of battery self-discharge. The optimized capacity testing process not only significantly shortens the time but also greatly reduces energy consumption, resulting in a substantial improvement in production efficiency.

[0010] Preferably, obtaining the first discharge capacity and the second total discharge capacity specifically includes the following steps: The battery is discharged at a constant current for the first time until the first cutoff voltage is reached, and the first discharge capacity is obtained.

[0011] Perform a full charge procedure on the battery; Perform a full discharge procedure on the battery to determine the second total discharge capacity. Perform a load adjustment procedure on the battery.

[0012] The existing technology's process of first fully charging, fully discharging, and then adjusting the load for capacity distribution has been abandoned, and the capacity distribution logic has been reconstructed.

[0013] Preferably, the current is 0.33. C ~1C .

[0014] Preferably, the first cutoff voltage is 2.5V. V ~2.8 V .

[0015] Preferably, the full charge step specifically involves: charging the battery with a constant current and constant voltage at a certain current; when the battery voltage reaches the second charging cutoff voltage, switching to the constant voltage charging stage, and continuing to charge until the current drops to the set cutoff value.

[0016] The steps to achieve full charging of the battery by dividing its capacity.

[0017] Preferably, the full discharge step specifically involves discharging the battery at a constant current until the third cutoff voltage is reached.

[0018] The steps to achieve full discharge of the battery by dividing its capacity.

[0019] Preferably, the load adjustment step is as follows: the battery is charged with a constant current and constant voltage at a certain current. When the battery voltage reaches the fourth cutoff voltage, it enters the constant voltage charging stage and continues charging until the current drops to the set cutoff value.

[0020] The load adjustment steps to achieve battery capacity grading.

[0021] Preferably, the cutoff value is set to 0.05. C ~0.1 C .

[0022] Preferably, constructing a relational model includes the following steps: Remove the discrete values ​​of the first discharge capacity and the total second discharge capacity from multiple sets; For multiple sets of first discharge capacities after removing discrete values, the maximum and minimum values ​​are obtained, and the range is calculated; Classified by the first discharge capacity range X The data range is then sequentially assigned to the cell and its second total discharge capacity data. X Same interval number Y Data groups, establish one-to-one data group pairs ( X i , Y i ); calculate X i The arithmetic mean of all first discharge capacities within the group is denoted as and calculation Y i The arithmetic mean of the total second discharge capacity within the group is denoted as . ; Using the average value of the first discharge capacity as the independent variable The average value of the second total discharge capacity Using as the dependent variable, establish a linear regression equation between the two variables.

[0023] This step effectively avoids interference from discrete values ​​and data noise, reduces errors, and improves the coefficient of determination.

[0024] Preferably, a resting step is also included.

[0025] Each time the battery is operated, a corresponding resting procedure is required, but this is not a key point and will not be elaborated upon. The advantages of this invention are as follows: It abandons the existing technology's steps of full charging, full discharging, and then load adjustment for capacity testing, and reconstructs the capacity testing logic. Instead, it utilizes the natural step of the battery's first factory discharge, achieving three benefits in one step. First, it can directly obtain key discharge data for modeling; second, based on the relational model, it can predict the battery's total capacity in real time and complete the core capacity testing judgment, thus completely eliminating the time-consuming full charging and full discharging steps in the existing process. Moreover, the battery state after the first factory discharge is exactly in a state of charge suitable for load adjustment, creating perfect conditions for subsequent steps. The entire process is interconnected and seamless, achieving comprehensive optimization of the capacity testing process in terms of efficiency, energy consumption, and operational smoothness. Attached Figure Description

[0026] Figure 1 This is a schematic flowchart of the battery capacity testing method in Embodiment 1 of the present invention; Figure 2 This is in Embodiment 1 of the present invention S Flowchart of 1; Figure 3 This is a fitted line graph of the first discharge capacity and the second total discharge capacity in Embodiment 2 of the present invention; Figure 4 This is a histogram of the error between the fitted second total discharge capacity and the second total discharge capacity measured when the battery is fully discharged, in Embodiment 2 of the present invention. Figure 5 This is a flowchart of existing technology capacity allocation; Figure 6 This is a voltage curve diagram of the capacity grading technology. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Example 1 See Figure 1 This embodiment requires a battery capacity grading method, including the following steps: S 1. Obtain the first discharge capacity and the second total discharge capacity after full discharge of multiple groups of pre-sized batteries; see reference. Figure 2 Specifically, it includes the following steps: S 10. Storage of battery 1 min .

[0029] S 11. with 0.33 C ~1 C The current during the first constant current discharge of the battery is 150. min To the first cutoff voltage V 2. The value varies slightly depending on the material system, but it is usually around 2.5. V ~2.8 V Perform the initial factory discharge procedure. Obtain the first discharge capacity. C 2.

[0030] S 12. Store batteries 5 min .

[0031] S 13. With 0.33~1 C The battery is charged with a constant current and constant voltage. When the battery voltage reaches the second charging cutoff voltage... V 4. The value varies slightly depending on the material system, but it is usually around 3.65. V ~3.8 V During this period, it transitions to a constant voltage charging phase, continuously charging for 200... min Until the current drops to 0.05 C ~0.1 C Set the cutoff value and execute the full charge step.

[0032] S 14. Store batteries 5 min .

[0033] S 15. with 0.33 C ~1 C The current discharges the battery at a constant current of 200. min To the third cutoff voltage V 6. The value varies slightly depending on the material system, but it is usually around 2.5. V ~2.8 V Perform the full discharge step to obtain the second total discharge capacity. C 6.

[0034] S 16. Store 5 batteries min .

[0035] S 17. with 0.33 C ~1 C The battery is charged with a constant current and constant voltage, and the battery voltage reaches the fourth cutoff voltage. V 8. The fourth cutoff voltage is required for the self-discharge test. SOC At the corresponding voltage, the system enters a constant voltage charging phase, continuing charging until the current drops to 0.05. C ~0.1 C Set the cutoff value and execute step 11.

[0036] S 18. Storage of battery 1 min .

[0037] See Table 1 below for details: Table 1

[0038] It is worth noting that, regarding the first discharge capacity C 2. Total discharge capacity of the second discharge C The acquisition of 6 can be displayed by the formation device when the battery is discharged, and multiple sets of data values ​​can be acquired. As this is existing technology, it will not be described in detail here.

[0039] S 2. Construct a model relating the first discharge capacity to the second total discharge capacity. Based on this model, the second total discharge capacity can be obtained from the battery's first discharge at the factory. This includes the following steps: S 20. Calculate the first discharge capacity for multiple groups respectively. C 2 and multiple groups of second discharge total capacity C The mean of 6 mean and standard deviation σ ,determination mean ±4 σ Values ​​outside the range are discrete values, which are interference factors and noise in the regression equation, and discrete values ​​are removed.

[0040] S 21. For multiple sets of first discharge capacities after removing discrete values. C 2. Find the maximum value C 2max and minimum value C 2min And calculate the range R , R = C 2max C 2min ,in,C 2max First discharge capacity C 2 maximum value, C 2min First discharge capacity C 2. Minimum value.

[0041] S 22. Based on the first discharge capacity C range of 2 R First, its numerical range is divided into 10 to 20 ordered intervals at equal intervals, and labeled sequentially as follows: X 1, X 2, ... X n For example, when the range R 1200 mAh At that time, it can be set to 100 mAh This is the group interval, thus forming 12 consecutive groups. C 2. Capacity range.

[0042] Then, each cell is divided according to its first discharge capacity. C 2. Measured values ​​are assigned to the corresponding values. X The interval; simultaneously, its corresponding second total discharge capacity. C 6 values, categorized with X Same interval number Y Data groups, labeled sequentially as Y 1, Y 2, ... Y n This establishes a one-to-one data pair. X i , Y i To ensure the statistical validity of the grouping results, each group is defined as follows: X Intervals and their corresponding Y The number of battery cells contained in a data set must not be less than 0.5% of the total number of battery cells. If the initial sample size of a set does not reach this threshold, it must be merged with adjacent sets until the minimum sample size requirement is met.

[0043] S 23. Calculate X i All first discharge capacities within the group C The arithmetic mean of 2 is denoted as . and calculation Y i Total second discharge capacity within the group C The arithmetic mean of 6 is denoted as This operation transforms the original discrete data points into a series of representative mean data points. , (), , )... ( , This step effectively avoids interference from discrete values ​​and data noise, reduces errors, and improves the coefficient of determination. The coefficient of determination is a core indicator for evaluating the goodness of fit of a regression model, quantifying the total second discharge capacity that the model can explain. C The proportion of fluctuations is based on existing technology.

[0044] S 24. With the first discharge capacity C 2. The mean is the independent variable. With the second total discharge capacity C 6 average Using the least squares method to fit a line graph and establish a linear regression equation between the two variables, the second total discharge capacity can be obtained based on the battery's first discharge at the factory.

[0045] S 3. Perform the first discharge of the un-rated battery before it leaves the factory to obtain the discharge capacity of the un-rated battery. Based on the relationship model, obtain the total discharge capacity of the un-rated battery. S 4. Charge and adjust the load of the un-capacitated battery to obtain the un-capacitated battery. SOC Voltage.

[0046] S 5. Complete the capacity testing of untested batteries.

[0047] For steps S 3~ S For items 4 and above, please refer to Table 1. A corresponding shelving operation is still required, but this is not the focus of this embodiment and will not be elaborated upon further.

[0048] In this embodiment, by studying the first discharge capacity and the second total discharge capacity of multiple groups of pre-sized batteries during their initial factory discharge, a relationship model between the first discharge capacity and the second total discharge capacity is constructed. This means that after obtaining the discharge capacity of unsized batteries during their first factory discharge, the total discharge capacity of unsized batteries can be obtained, thus directly omitting the full charge and full discharge steps. This is because the load adjustment step... SOC The range is relatively low, only 5%-20% of battery self-discharge. The optimized capacity testing process not only significantly shortens the time but also greatly reduces energy consumption, resulting in a substantial improvement in production efficiency.

[0049] Furthermore, this embodiment abandons the existing technology's steps of full charging, full discharging, and then load adjustment for capacity testing, and reconstructs the capacity testing logic. Instead, it utilizes the natural step of the battery's first factory discharge to achieve three goals at once. First, it can directly obtain key discharge data for modeling; second, based on the relational model, it can predict the battery's total capacity in real time and complete the core capacity testing judgment, thereby completely eliminating the time-consuming full charging and full discharging steps in the existing process. Moreover, the battery state after the first factory discharge is exactly in a state of charge suitable for load adjustment, creating perfect conditions for subsequent steps. The entire process is interconnected and completed in one go, achieving comprehensive optimization of the capacity testing process in terms of efficiency, energy consumption, and operational smoothness.

[0050] Example 2 This embodiment, based on Embodiment 1, provides a battery capacity testing method for a specific application of a lithium iron phosphate battery system. First, capacity testing is performed according to the process shown in Table 1 to obtain several sets of first discharge capacities. C 2. Total discharge capacity of the second discharge C 6. Refer to Table 2: Table 2

[0051] Secondly, the first discharge capacity is calculated separately. C 2. Total discharge capacity of the second discharge C The mean of 6 mean and standard deviation σ ,exist mean ±4 σ The values ​​outside the range are discrete values. After removing these, there are a total of 1073 data entries remaining.

[0052] Next, calculate the first discharge capacity from the remaining data. C 2 maximum values C 2max 41403 mAh and first discharge capacity C 2 minimum value C 2min It is 39897.5 mAh And calculate the range R = C 2max C 2min =1505.5 mAh .

[0053] Then, based on the range R The size of the first discharge capacity C 2 with 100 mAh Divide the interval into zones; correspondingly, the second total discharge capacity C 6 is also partitioned in the same way.

[0054] Then, the first discharge capacity of each interval is calculated. C 2. Total discharge capacity of the second discharge C The average value of 6 is shown in Table 3: Table 3

[0055] It is worth noting that in Table 3, when the number of cells in a certain interval is too small, the data after merging it with the adjacent intervals into one group is displayed.

[0056] See Figure 3 Finally, based on the first discharge capacity C 2. The mean is the independent variable. x With the second total discharge capacity C 6. The mean is the dependent variable. y Using the least squares method, a fitted line plot is generated, and a linear regression equation between the two variables is established, yielding the following formula: y =0.9644 x +99913. Upon review, the coefficient of determination is as high as 99.4%, which is sufficient to demonstrate that the independent and dependent variables are highly linearly correlated.

[0057] See Figure 4 Furthermore, the first discharge capacity measured during the first discharge of the ungraded battery before it leaves the factory is used as the independent variable. x Substitute into the linear regression equation: y =0.9644 x +99913, obtain the fitted second total discharge capacity, then calculate the error value between the fitted second total discharge capacity and the second total discharge capacity measured at full discharge of the battery, and obtain Table 4: Table 4

[0058] It can be concluded that the error values ​​are all controlled within ±0.6%, indicating high fitting accuracy.

[0059] Therefore, for the lithium iron phosphate battery system without capacity testing, the first discharge at the factory is performed to obtain the first discharge capacity of the battery. x Substituting into the linear regression equation: y =0.9644 x +99913, after obtaining the total discharge capacity of the battery, proceed to the load adjustment step. The entire process omits the full charge and full discharge stages. For this lithium iron phosphate battery system, the capacity assessment process is from 260... min Reduced to 70 min This reduces the time by about 70%, greatly saving process time and reducing equipment energy consumption.

[0060] It is worth mentioning that the least squares method is a mathematical optimization technique that finds the best function match for the data by minimizing the sum of squares of the errors. As it is existing technology, it is not the focus of this embodiment and will not be described in detail.

[0061] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A battery capacity testing method, characterized in that, Includes the following steps: Obtain the first discharge capacity and the second total discharge capacity of multiple groups of pre-sized batteries during their first discharge at the factory; A model relating the first discharge capacity to the second total discharge capacity is constructed. Based on this model, the second total discharge capacity can be obtained from the battery's first discharge at the factory. For the first discharge of un-rated batteries, obtain the discharge capacity of the un-rated batteries, and based on the relationship model, obtain the total discharge capacity of the un-rated batteries; Charge and adjust the load of un-capacitated batteries to obtain un-capacitated batteries. SOC Voltage; Complete the capacity testing of untested batteries.

2. The battery capacity assessment method according to claim 1, characterized in that, Obtaining the first discharge capacity and the second total discharge capacity specifically includes the following steps: The battery is discharged at a constant current for the first time until the first cutoff voltage is reached, and the first discharge capacity is obtained. Perform a full charge procedure on the battery; Perform a full discharge step on the battery to obtain the second total discharge capacity; Perform a load adjustment procedure on the battery.

3. The battery capacity testing method according to claim 2, characterized in that, A given current of 0.33 C ~1 C .

4. The battery capacity testing method according to claim 2, characterized in that, The first cutoff voltage is 2.

5. V ~2.8 V .

5. The battery capacity assessment method according to claim 2, characterized in that, The full charge process is as follows: the battery is charged with a constant current and constant voltage at a certain current. When the battery voltage reaches the second charging cutoff voltage, it enters the constant voltage charging stage and continues charging until the current drops to the set cutoff value.

6. The battery capacity testing method according to claim 2, characterized in that, The full discharge procedure is as follows: discharge the battery with a constant current until the third cutoff voltage.

7. The battery capacity assessment method according to claim 2, characterized in that, The specific loading steps are as follows: charge the battery with a constant current and constant voltage at a certain current. When the battery voltage reaches the fourth cutoff voltage, switch to the constant voltage charging stage and continue charging until the current drops to the set cutoff value.

8. The battery capacity testing method according to claim 7, characterized in that, Set the cutoff value to 0.05 C ~0.1 C .

9. The battery capacity testing method according to claim 1, characterized in that, Building a relational model involves the following steps: Remove the discrete values ​​of the first discharge capacity and the total second discharge capacity from multiple sets; For multiple sets of first discharge capacities after removing discrete values, the maximum and minimum values ​​are obtained, and the range is calculated; Classified by the first discharge capacity range X The data range is then sequentially assigned to the cell and its second total discharge capacity data. X Same interval number Y Data groups, establishing one-to-one data group pairs ( X i , Y i ); calculate X i The arithmetic mean of all first discharge capacities within the group is denoted as and calculation Y i The arithmetic mean of the total second discharge capacity within the group is denoted as . ; Using the average value of the first discharge capacity as the independent variable The average value of the second total discharge capacity Using as the dependent variable, establish a linear regression equation between the two variables.

10. The battery capacity testing method according to claim 1, characterized in that, It also includes a shelving step.

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