Battery capacity grading capacity compensation method and lithium battery
By analyzing the temperature and capacity during the capacity grading process of lithium batteries, a capacity compensation formula was derived, which solved the problem of inconsistent battery capacity caused by temperature deviation and improved the uniformity and reliability of battery capacity.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-28
- Publication Date
- 2026-03-13
AI Technical Summary
In the current lithium battery capacity grading process, temperature deviations can lead to inconsistent battery capacities, which can easily cause overcharging or over-discharging, affecting the battery pack's lifespan and safety.
By analyzing the process capability of historical cell grading temperatures and capacities, calculating temperature rise and capacity growth rate, and deriving a capacity compensation formula, a capacity compensation formula is used for capacity compensation during mass production line grading to improve battery capacity consistency.
It effectively compensates for the unutilized capacity caused by temperature deviations, avoids the dispersion of battery capacity levels, and improves the capacity consistency and reliability of lithium batteries.
Smart Images
Figure CN121658771A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of battery technology, and in particular to a battery capacity compensation method and a lithium battery. Background Technology
[0002] Throughout the lithium battery manufacturing process, the effectiveness of each step significantly impacts the battery's electrochemical performance. Capacity grading is one of the key processes in lithium battery manufacturing. Based on the measurement and analysis of battery charge-discharge characteristics, capacity grading screens and classifies batteries to eliminate substandard batteries through precise measurement and rigorous screening. This improves the consistency and reliability of battery packs, ensuring smoother assembly and adaptation to different application scenarios, and optimizing resource allocation.
[0003] The capacity rating of lithium-ion batteries is highly sensitive to temperature, and batteries made with different cathode materials exhibit varying degrees of capacity utilization. Under the same capacity rating conditions, the capacity of a battery will show a certain degree of ramp-up in the first few cycles after the initial capacity rating. Once the cathode material has fully utilized its capacity, the capacity will gradually stabilize until it gradually decreases with increasing cycle count. Archiving batteries with similar actual capacities ensures balanced performance in the assembled battery pack. Matching the capacity of batteries maximizes overall energy utilization and prevents premature failure of some cells due to differences in individual cell counts, thereby improving the cycle life and reliability of the battery pack.
[0004] In existing battery manufacturing processes, the temperature control methods commonly used in the capacity grading process mainly include internal circulating cooling water and internal exhaust fans. While these methods can effectively control the ambient temperature during the capacity grading process, the differences in storage locations cause temperature deviations between batteries during grading. This results in some batteries having the correct capacity, but due to their capacity being too high or too low, the overall battery capacity is not concentrated. Batteries with poor consistency are prone to overcharging and over-discharging during charging and discharging, leading to shortened battery life and even safety hazards. Therefore, improving the consistency of battery capacity during grading requires further research. Summary of the Invention
[0005] Based on this, the purpose of the present invention is to provide a battery capacity compensation method and a lithium battery, which can not only compensate for the portion of the battery capacity that is not fully utilized due to temperature deviation during the capacity grading process, but also avoid the phenomenon of battery capacity dispersion, thereby improving the capacity consistency and reliability of lithium batteries.
[0006] To achieve the above objectives, the present invention adopts the following technical solution: This invention first provides a battery capacity compensation method, which includes the following steps: S1. Obtain the grading temperature and grading capacity of multiple historical battery cells; S2. Perform process capability analysis on the capacity rating and capacity rating of the multiple historical cells to obtain the average capacity rating and average capacity rating of the multiple historical cells; S3. Using the average capacity-dividing temperature and average capacity-dividing capacity as benchmark values, calculate the temperature rise and capacity growth rate of each historical cell, obtain the relationship between the capacity growth rate and the temperature rise, and derive the capacity compensation formula based on the relationship. S4. When dividing capacity on the mass production line, perform capacity compensation on the cells that have just been divided according to the capacity compensation formula.
[0007] As a further improvement to the above-mentioned solution of the present invention, in step S1, the specifications of the multiple historical cells are the same, and the multiple historical cells satisfy the following: the weight of each historical cell before one liquid injection is the weight of the standard cell ±5g.
[0008] As a further improvement to the above-mentioned solution of the present invention, in step S1, the capacity testing temperature is the average temperature of the battery cell during the discharge step of the historical battery cell in the capacity testing process.
[0009] As a further improvement to the above-described solution of the present invention, the average temperature of the battery cell is the average temperature of the battery cell surface.
[0010] As a further improvement to the above-mentioned solution of the present invention, in step S1, the capacity grading is the capacity released by the historical cell during the discharge step in the capacity grading process.
[0011] As a further improvement to the above-mentioned solution of the present invention, in step S1, the number of historical battery cells is 1,000-130,000.
[0012] As a further improvement to the above-described solution of the present invention, step S3, which involves obtaining the relationship between the capacity growth rate and the temperature rise and deriving the capacity compensation formula based on the relationship, includes: Plot a graph showing the relationship between capacity growth rate and temperature rise, with temperature rise on the horizontal axis and capacity growth rate on the vertical axis. Linear fitting and regression analysis were performed on the relationship graph to obtain the linear regression equation. ,in, f (T 1 ) For capacity growth rate, T 1 represents the temperature rise. k The slope b It is a constant; Based on the linear regression equation, derive the capacity compensation formula:
[0013] in, f(T 2 ) To compensate for capacity, CapFor cell capacity, The average volumetric temperature, T 2 represents the average temperature of the battery cell.
[0014] As a further improvement to the above-mentioned solution of the present invention, the cell capacity is the cell capacity during the discharge step when the cell that has just completed capacity testing is tested on the mass production line; the average cell temperature is the average cell temperature during the discharge step when the cell that has just completed capacity testing is tested on the mass production line.
[0015] As a further improvement to the above-mentioned solution of the present invention, the specifications of the battery cell that has just completed capacity testing are the same as those of the historical battery cell.
[0016] The present invention also provides a lithium battery, which is obtained based on the battery capacity compensation method described above.
[0017] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a method for compensating battery capacity during capacity grading based on temperature. It involves analyzing the process capability of battery capacity grading and temperature data. First, baseline values for grading temperature and capacity are determined. The temperature rise and capacity growth rate relative to these baseline values are calculated, and a preliminary linear relationship equation is obtained through graphing. Then, outliers are eliminated using this linear relationship equation, and regression analysis is performed to derive a linear regression equation. Finally, a capacity compensation formula is applied in the capacity grading system using this formula. This invention not only compensates for the portion of the battery's capacity not fully utilized due to temperature deviations during capacity grading but also avoids the phenomenon of inconsistent battery capacity levels, improving the consistency of lithium battery capacity. Attached Figure Description
[0018] Figure 1 This is a flowchart of a battery capacity compensation method proposed in an embodiment of the present invention; Figure 2 This is a graph showing the results of process capability analysis of lithium iron phosphate batteries at the capacity rating temperature in an embodiment of the present invention. Figure 3 This is a graph showing the process capability analysis results of the capacity testing of lithium iron phosphate batteries in an embodiment of the present invention. Figure 4 This is a graph showing the relationship between the actual capacity growth rate and temperature rise of the lithium iron phosphate battery in this embodiment of the invention. Figure 5 This is a fitted curve of the actual capacity growth rate and temperature rise of the lithium iron phosphate battery in the embodiments of the present invention; Figure 6 This is a residual graph showing the actual capacity growth rate of the lithium iron phosphate battery in an embodiment of the present invention. Detailed Implementation
[0019] To facilitate understanding of the present invention, a more comprehensive description will be given below with reference to specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention.
[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.
[0021] Reference Figure 1 This embodiment proposes a battery capacity compensation method, applicable to lithium iron phosphate batteries, etc., which includes the following steps: S1. Obtain the grading temperature and grading capacity of multiple historical cells.
[0022] In this embodiment, when selecting historical cells, it should be ensured that the specifications of the historical cells are the same, and the weight of each historical cell before one electrolyte filling is ±5g of the standard cell weight, in order to minimize the capacity error caused by areal density. The number of historical cells is 1,000-130,000.
[0023] The capacity rating temperature is the average temperature of the battery cell during the discharge steps of the capacity rating process in history. The average cell temperature is the average temperature of the cell surface. The capacity rating capacity is the capacity discharged by the battery cell during the discharge steps of the capacity rating process in history.
[0024] S2. Perform process capability analysis on the capacity rating and capacity rating of multiple historical cells to obtain the average capacity rating and average capacity rating of multiple historical cells.
[0025] S3. Using the average capacity-sharing temperature and average capacity-sharing capacity as benchmarks, calculate the temperature rise and capacity growth rate of each historical cell, obtain the relationship between the actual capacity growth rate and the temperature rise, and derive the capacity compensation formula based on the relationship. Specifically: A graph showing the relationship between temperature rise and capacity growth rate was plotted with temperature rise on the horizontal axis and capacity growth rate on the vertical axis. The graph shows that temperature rise and capacity growth rate are basically linearly correlated. However, due to the large sample size, the graph is initially coarse. The data needs to be further optimized and fitted to screen out outliers and data with large differences. Linear fitting and regression analysis were performed on the relationship graph to obtain the linear regression equation. ,in, f(T 1 ) For capacity growth rate, T 1 represents the temperature rise. k The slope b It is a constant; Based on the linear regression equation, derive the capacity compensation formula:
[0026] in, f(T 2 ) To compensate for capacity; Cap The cell capacity is the average cell capacity, which is the cell capacity during the discharge step when the cell that has just completed capacity testing is tested on the mass production line. This is the average volumetric temperature; T 2 represents the average cell temperature, which is the average cell temperature during the discharge step when the cells have just completed capacity testing on the mass production line.
[0027] S4. When dividing capacity on the mass production line, perform capacity compensation on the cells that have just been divided according to the capacity compensation formula.
[0028] After the battery capacity assessment system receives the input capacity compensation formula, it automatically performs corresponding capacity compensation based on the actual capacity data of each battery, and finally uploads the compensated battery capacity data to the database. The battery cells that have just undergone capacity assessment have the same specifications as the historical cells.
[0029] Next, we will take a lithium iron phosphate battery as an example to further illustrate the present invention.
[0030] First, collect the capacity grading data for a batch of the same historical lithium iron phosphate batteries: the capacity grading temperature and capacity grading during the discharge process.
[0031] A process capability analysis was performed on the capacity rating data of this batch of lithium iron phosphate batteries, such as... Figure 2 , Figure 3 As shown.
[0032] The average capacity rating of this batch of lithium iron phosphate batteries was found to be 37.2℃ and the average capacity rating to be 155Ah. Using these average capacity ratings as a baseline, the temperature rise and actual capacity growth rate of each lithium iron phosphate battery relative to the baseline were calculated, and a graph showing the relationship between temperature rise and actual capacity growth rate was plotted. Figure 4 As shown.
[0033] from Figure 4 It can be seen that the temperature rise is basically linearly correlated with the actual capacity growth rate. However, due to the large sample size, the graph is rather coarse, and the original data needs further optimization and fitting, such as... Figure 5 As shown.
[0034] The predicted data from the initially obtained linear relationship equation is compared with the actual data to screen out outliers and data with large discrepancies. Finally, regression analysis is performed using the optimized data. Figure 6 As shown.
[0035] Because the data in the regression analysis was processed, overfitting caused the normal probability plot in the residual analysis graph to deviate from its beginning and end. Based on the fitted plot, the linear regression equation is: f(T 1 )= 0.005314 T 1-0.000047 Thus, the capacity compensation formula is derived: f(T 2 )=Cap / {f(T 1 )+1} =Cap / (0.0005314(T2-37.2)+0.99936) ≈Cap / (0.0053T2+0.8) in: f(T 1 ) For capacity growth rate, T 1 represents the temperature rise. f(T 2 ) To compensate for capacity, Cap For the discharge step cell capacity, T 2 represents the average temperature during the discharge process.
[0036] Four cells were randomly selected from the above batch of cells as capacity compensation targets. The capacity of these four cells is 152Ah, 155.5Ah, 156Ah, and 159Ah, respectively. The capacity compensation formula obtained by fitting was used to compensate the four cells. The comparison results of the capacity data before and after compensation are shown in the table below.
[0037]
[0038] As shown in Table 1, after using the method of the present invention to perform capacity compensation on lithium iron phosphate batteries, the concentration of capacity of the batteries is improved, the tolerance of the batteries is significantly reduced, and the capacity consistency and reliability of the batteries are improved.
[0039] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.
[0040] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.
Claims
1. A battery capacity compensation method, characterized in that, It includes the following steps: S1. Obtain the grading temperature and grading capacity of multiple historical battery cells; S2. Perform process capability analysis on the capacity rating and capacity rating of the multiple historical cells to obtain the average capacity rating and average capacity rating of the multiple historical cells; S3. Using the average capacity-dividing temperature and average capacity-dividing capacity as benchmark values, calculate the temperature rise and capacity growth rate of each historical cell, obtain the relationship between the capacity growth rate and the temperature rise, and derive the capacity compensation formula based on the relationship. S4. When dividing capacity on the mass production line, perform capacity compensation on the cells that have just been divided according to the capacity compensation formula.
2. The battery capacity compensation method according to claim 1, characterized in that, In step S1, the specifications of the multiple historical cells are the same, and the multiple historical cells satisfy the following: the weight of each historical cell before one liquid injection is the weight of the standard cell ±5g.
3. The battery capacity compensation method according to claim 1, characterized in that, In step S1, the capacity testing temperature is the average cell temperature during the discharge step of the historical cell in the capacity testing process.
4. The battery capacity compensation method according to claim 3, characterized in that, The average temperature of the battery cell is the average temperature of the cell surface.
5. The battery capacity compensation method according to claim 1, characterized in that, In step S1, the capacity grading is the capacity released by the historical cell during the discharge step in the capacity grading process.
6. The battery capacity compensation method according to claim 1, characterized in that, In step S1, the number of historical battery cells is 1,000-130,000.
7. The battery capacity compensation method according to claim 1, characterized in that, In step S3, obtaining the relationship between the capacity growth rate and the temperature rise, and deriving the capacity compensation formula based on the relationship, includes: Plot a graph showing the relationship between capacity growth rate and temperature rise, with temperature rise on the horizontal axis and capacity growth rate on the vertical axis. Linear fitting and regression analysis were performed on the relationship graph to obtain the linear regression equation. ,in, f(T 1 ) For capacity growth rate, T 1 represents the temperature rise. k The slope b It is a constant; Based on the linear regression equation, derive the capacity compensation formula: in, f(T 2 ) To compensate for capacity, Cap For cell capacity, The average volumetric temperature, T 2 represents the average temperature of the battery cell.
8. The battery capacity compensation method according to claim 7, characterized in that, The cell capacity is the cell capacity during the discharge step when the cell that has just completed capacity testing is tested on the mass production line; the average cell temperature is the average cell temperature during the discharge step when the cell that has just completed capacity testing is tested on the mass production line.
9. The battery capacity compensation method according to claim 1, characterized in that, The battery cell that has just completed capacity testing has the same specifications as the historical battery cell.
10. A lithium battery, characterized in that, It is based on the battery capacity compensation method as described in any one of claims 1-9.