Methods for Online Testing of Battery Performance Consistency Among Sodium-Lithium Hybrid Battery Packs

Abstract

This invention relates to the field of battery consistency testing technology, specifically a method for online testing of battery performance consistency among sodium-lithium hybrid battery packs. The method includes the following steps: acquiring charging data of the cells during vehicle charging; sequentially numbering each cell and determining its type; calculating the voltage and internal resistance of the sodium-ion cells, and the voltage and temperature of the lithium-ion cells, based on the charging data, to determine the consistency between the sodium-ion and lithium-ion cells. If both the consistency of the lithium-ion cells and the consistency of the sodium-ion cells in the battery pack meet the requirements, then the battery pack meets the consistency requirements; otherwise, it does not. This invention can effectively improve the accuracy of testing battery performance consistency among sodium-lithium hybrid battery packs.

Description

Technical Field

[0001] This invention relates to the field of battery consistency testing technology, specifically a method for online testing of battery performance consistency among sodium-lithium hybrid battery packs. Background Technology

[0002] Currently, power batteries are used more and more widely. Individual cells must be connected in series / parallel to form battery packs to meet the voltage, capacity, and other requirements of applications. From individual cells to battery packs, the performance of individual cells usually needs to be highly consistent within the same pack for the battery pack to fully perform. Good cell consistency includes highly overlapping charge-discharge curves, highly consistent internal resistance, and very synchronized degradation under the same test conditions. Otherwise, during the use of the battery pack, overcharging or over-discharging of a single cell can easily lead to performance degradation and accelerated deterioration, causing the entire battery pack to fail quickly. Currently, there is no unified standard for evaluating the consistency of battery packs composed of different cells. Most current methods use capacity matching, which involves conducting multiple rounds of charge-discharge tests to obtain the average capacity of the cells, and then matching cells with similar average capacities into packs. This method is too simplistic, only considering the current capacity of the cells. In actual use, due to the lack of testing of other internal electrochemical parameters, the heat generation and capacity degradation rate of each individual cell will differ during reuse, quickly leading to new inconsistencies. This means that the battery packs composed of the selected cells cannot achieve their maximum performance. To address the problems in the prior art, patent CN116184249A discloses a method, system, and medium for judging battery pack consistency. By using the clustering of points representing multiple battery performance indicators in a multidimensional space as an indicator to describe battery pack consistency, the consistency between batteries is abstracted as the aggregation between points in a multidimensional space, so that the various performance indicators of each individual battery in the battery pack tend to be consistent, maximizing the performance of the battery pack.

[0003] In practical applications, sodium-ion batteries offer advantages over lithium-ion batteries, including lower cost, higher safety, stronger low-temperature performance, and superior rate capability. However, due to their lower energy density and theoretical number of charge-discharge cycles, sodium-ion batteries are significantly heavier than lithium-ion batteries to achieve the same driving range in the power battery field. This increased weight places higher demands on vehicle structure and other aspects. To address this issue, some manufacturers have introduced sodium-lithium hybrid batteries. However, testing sodium-lithium hybrid batteries using existing methods suffers from poor accuracy due to the different battery characteristics of sodium-ion and lithium-ion batteries, a problem that urgently needs to be solved. Summary of the Invention

[0004] To avoid and overcome the technical problems existing in the prior art, this invention provides a method for online detection of battery performance consistency among sodium-lithium hybrid battery packs. This invention can effectively improve the accuracy of detecting battery performance consistency among sodium-lithium hybrid battery packs.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for online detection of battery performance consistency among sodium-lithium hybrid battery packs includes the following steps:

[0007] S1. Obtain the charging data of the battery cells when the vehicle is charging;

[0008] S2. Number each cell sequentially and determine the type of each cell;

[0009] S3. Calculate the voltage and internal resistance of the sodium-ion battery cell using charging data. If the voltage of the sodium-ion battery cell is higher or lower than the set voltage value and the internal resistance of the sodium-ion battery cell is the highest among all sodium-ion battery cells in the vehicle, then the voltage consistency and internal resistance consistency of the sodium-ion battery cell do not meet the requirements.

[0010] S4. Calculate the voltage and temperature of the lithium-ion cell using the charging data. If the voltage of the lithium-ion cell is higher or lower than the set voltage value and the temperature of the sodium-ion cell is higher or lower than the set temperature value, then the consistency of the lithium-ion cell does not meet the requirements. When the consistency of both the lithium-ion cells and the sodium-ion cells in the battery pack meets the requirements, then the consistency of the battery pack meets the requirements; otherwise, it does not.

[0011] As a further aspect of the present invention: the charging data includes the temperature, voltage and current of the battery cell during charging, which are timestamped.

[0012] As a further aspect of the present invention, lithium-ion cells and sodium-ion cells can be distinguished by checking the markings on the cell.

[0013] As a further aspect of the present invention: the voltage consistency judgment step of sodium-ion cells in step S3 is as follows: S3A1, firstly calculate the average voltage and standard deviation of all sodium-ion cells at the same time, then calculate the set voltage value using the average voltage and standard deviation, the set voltage value being [U n，t，max U n，t，min ], where U n，t，max U represents the upper limit of the voltage value set at time t for a sodium-ion battery cell. n，t，min This indicates the lower limit of the voltage value set at time t for the sodium-ion battery cell. The subscript n represents the sodium-ion battery cell, the subscript t represents the time t, the subscript max represents the upper limit, and the subscript min represents the lower limit.

[0014] S3A2. Compare the voltage of the sodium-ion battery cell to be evaluated at the same moment with the set voltage value. If the voltage of the sodium-ion battery cell to be evaluated is higher than U... n，t，max or below U n，t，min If the voltage consistency of the sodium-ion battery cell to be evaluated does not meet the requirements, then the evaluation does not meet the requirements.

[0015] As a further aspect of the present invention, the formula for calculating the set voltage value is as follows:

[0016] U n，t，max =U n，t，avg +3U n，t，std

[0017] U n，t，min =U n，t，avg -3U n，t，std

[0018] Among them, U n，t，avg U represents the average voltage of all sodium-ion batteries in the vehicle at time t; n，t，std This represents the standard deviation of the voltage of all sodium-ion batteries in the vehicle at time t.

[0019] As a further aspect of the present invention: the step of determining the internal resistance consistency of the sodium-ion battery cell in step S3 is as follows:

[0020] S3B1. Calculate the instantaneous internal resistance of each sodium-ion battery cell. The formula for calculating the instantaneous internal resistance is as follows:

[0021]

[0022] Where, r i，t，0 U represents the instantaneous internal resistance of the i-th sodium-ion battery cell at time t; i，t U represents the voltage of the i-th sodium-ion battery cell at time t; i，t-1 I represents the voltage of the i-th sodium-ion battery cell at time t-1; i，t I represents the current of the i-th sodium-ion battery cell at time t; i，t-1 This represents the current of the i-th sodium-ion battery cell at time t-1;

[0023] S3B2. Calculate the weighted internal resistance of the sodium-ion battery cell. The formula for calculating the weighted internal resistance is as follows:

[0024] R i，t+1 =0.999R i，t +0.001r i，t，0

[0025] Among them, R i,t+1 R represents the weighted internal resistance of the i-th sodium-ion battery cell at time t+1; i,t This represents the weighted internal resistance of the i-th sodium-ion battery cell at time t; when ri,t,0 When R is 0 or does not exist at the initial time 0, i,1 =R i,0 =0.35Ω.

[0026] As a further aspect of the present invention: the temperature consistency judgment step of the lithium-ion battery cell in step S4 is as follows:

[0027] S4A1. First, calculate the mean temperature and standard deviation of all lithium-ion cells at the same time. Then, calculate the set temperature value using the mean temperature and standard deviation. The set temperature value is [T]. L，t,max T L，t,min ], where T L，t,max T represents the upper limit of the temperature set at time t for a lithium-ion battery cell. L，t，min This represents the lower limit of the temperature set at time t for a lithium-ion battery cell. The subscript L indicates the lithium-ion battery cell, the subscript t indicates that t is the time, the subscript max indicates the upper limit, and the subscript min indicates the lower limit.

[0028] S4A2. Compare the temperature of the lithium-ion cell to be evaluated with the set temperature value at the same moment. If the temperature of the lithium-ion cell to be evaluated is higher than T... L，t，max or below T L，t，min If the temperature consistency of the lithium-ion cell to be evaluated does not meet the requirements, then the evaluation does not meet the requirements.

[0029] As a further aspect of the present invention, the formula for calculating the set temperature value is as follows:

[0030] T L,t,max =T L,t,avg +3T L,t,std

[0031] T L,t,min =T L,t,avg -3T L,t,std

[0032] Among them, T L，t，avg T represents the average temperature of all lithium-ion cells in the vehicle at time t; L，t,std This represents the standard deviation of temperature of all lithium-ion cells in the vehicle at time t.

[0033] As a further aspect of the present invention: the step of determining the voltage consistency of the lithium-ion battery cell in step S4 is the same as the step of determining the voltage consistency of the sodium-ion battery cell in step S3.

[0034] Compared with the prior art, the beneficial effects of the present invention are:

[0035] 1. Based on the different characteristics of sodium-ion cells and lithium-ion cells, this invention uses different methods to determine their inter-group consistency.

[0036] 2. Compared with the traditional method that mainly relies on voltage to determine the consistency between groups, our invention combines temperature and internal resistance to assist in the judgment, thereby improving accuracy.

[0037] 3. The present invention takes into account the time interval of the actual vehicle data upload in the calculation and performs smoothing processing on the internal resistance, which makes the solution more operable. Attached Figure Description

[0038] Figure 1 This diagram illustrates the main detection steps of the present invention.

[0039] Figure 2 This is a graph showing the change in internal resistance of the sodium-ion battery cell in this invention.

[0040] Figure 3 This is a voltage variation diagram of the sodium-ion battery cell in this invention.

[0041] Figure 4 This is a temperature change diagram of the lithium-ion battery cell in this invention.

[0042] Figure 5 This is a voltage variation diagram of the lithium-ion battery cell in this invention. Detailed Implementation

[0043] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0044] Please see Figures 1-5 In this embodiment of the invention, the method for online detection of battery performance consistency among sodium-lithium hybrid battery packs collected charging data at multiple time points. The charging data for the first 5 time points corresponding to sodium-ion cells are shown in Tables 1 and 2, and the charging data for the first 4 time points corresponding to lithium-ion cells are shown in Tables 3 and 4.

[0045] Table 1 Current and voltage data of sodium-ion batteries

[0046]

[0047] Table 2 Internal resistance data of sodium-ion battery cells

[0048]

[0049] In Tables 1 and 2, "time" represents the charging time, and Na_1, Na_2, Na_3, and Na_4 represent the numbers of the sodium-ion battery cells, respectively.

[0050] Table 3 Voltage data of lithium-ion cells

[0051]

[0052] Table 4 Temperature data of lithium-ion cells

[0053]

[0054] In Tables 3 and 4, "time" represents the charging time, and Li_1, Li_2, Li_3, and Li_4 represent the numbers of the lithium-ion cells, respectively.

[0055] The voltage consistency and internal resistance consistency of the sodium-ion battery cell are calculated and judged according to the above steps. The internal resistance change of the sodium-ion battery cell is as follows: Figure 2 As shown, the voltage change of the sodium-ion battery cell is as follows: Figure 3 As shown. By Figure 2 and Figure 3 As shown, the voltage variation of the sodium-ion battery cell did not exceed the set voltage value, and the sodium-ion battery wire did not exhibit voltage consistency issues, i.e., there were no voltage outliers. Voltage outliers occur when the voltage deviates from the set voltage range. The internal resistance of the sodium-ion battery cell changed smoothly, therefore, the sodium-ion battery cell did not exhibit internal resistance consistency issues. In conclusion, the battery cells used in this experiment did not have any inconsistency issues.

[0056] The voltage consistency and internal resistance consistency of the lithium-ion battery cell are calculated and judged according to the above steps. The temperature change of the lithium-ion battery cell is as follows. Figure 4 As shown, the voltage change of a lithium-ion battery cell is as follows: Figure 5 As shown. By Figure 4 and Figure 5 As shown, the lithium-ion cells in Section 4 exhibit both voltage and temperature outliers. Therefore, the lithium-ion cell modules show significant inconsistencies. Considering the inconsistencies between the sodium-ion and lithium-ion cell modules, we conclude that the overall consistency of this hybrid battery pack is poor.

[0057] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for online detection of battery performance consistency among sodium-lithium hybrid battery packs, characterized in that, Includes the following steps: S1. Obtain the charging data of the battery cells when the vehicle is charging; S2. Number each cell sequentially and determine the type of each cell; S3. Calculate the voltage and internal resistance of the sodium-ion battery cell using charging data. If the voltage of the sodium-ion battery cell is higher or lower than the set voltage value and the internal resistance of the sodium-ion battery cell is the highest among all sodium-ion battery cells in the vehicle, then the consistency of the sodium-ion battery cell does not meet the requirements. S4. Calculate the voltage and temperature of the lithium-ion cell using charging data. If the voltage of the lithium-ion cell is higher or lower than the set voltage value and the temperature of the lithium-ion cell is higher or lower than the set temperature value, then the consistency of the lithium-ion cell does not meet the requirements. When the consistency of both the lithium-ion cells and the sodium-ion cells in the battery pack meets the requirements, then the consistency of the battery pack meets the requirements; otherwise, it does not. The formula for calculating the set voltage value is as follows: in, U n,t,avg This indicates that all sodium-ion batteries in the vehicle are in t The average voltage at any given time; U n,t,std This indicates that all sodium-ion batteries in the vehicle are in t The standard deviation of voltage at any given time; The steps for determining the internal resistance consistency of sodium-ion cells in step S3 are as follows: S3B1. Calculate the instantaneous internal resistance of each sodium-ion battery cell. The formula for calculating the instantaneous internal resistance is as follows: in, r i,t,0 Indicates the first i A sodium-ion battery cell in t Instantaneous internal resistance at a given moment; U i,t Indicates the first i A sodium-ion battery cell in t Voltage at any given moment; U i,t-1 Indicates the first i A sodium-ion battery cell in t Voltage at time -1; I i,t Indicates the first i A sodium-ion battery cell in t Current at any given moment; I i,t-1 Indicates the first i A sodium-ion battery cell in t Current at time -1; S3B2. Calculate the weighted internal resistance of the sodium-ion battery cell. The formula for calculating the weighted internal resistance is as follows: in, R i,t+1 Indicates the first i A sodium-ion battery cell in t Weighted internal resistance at time +1; R i,t Indicates the first i A sodium-ion battery cell in t Weighted internal resistance at time; when r i,t,0 If it is 0 or does not exist at the initial time 0, R i,1 = R i,0 =0.35 Ω .

2. The method for online detection of battery performance consistency among sodium-lithium hybrid battery packs according to claim 1, characterized in that, The charging data includes timestamped temperature, voltage, and current of the battery cell during charging.

3. The method for online detection of battery performance consistency among sodium-lithium hybrid battery packs according to claim 2, characterized in that, You can distinguish between lithium-ion and sodium-ion battery cells by checking the markings on the cells.

4. The method for online detection of battery performance consistency among sodium-lithium hybrid battery packs according to claim 3, characterized in that, The steps for determining the voltage consistency of sodium-ion cells in step S3 are as follows: S3A1. First, calculate the mean voltage and standard deviation of all sodium-ion cells at the same time. Then, calculate the set voltage value using the mean voltage and standard deviation. The set voltage value is [[]]. U n,t,max , U n,t,min ],in, U n,t,max This indicates that sodium-ion cells are in t The upper limit of the voltage value set at any time. U n,t,min This indicates that sodium-ion cells are in t The lower limit of the voltage value set at any time, subscript n Indicates sodium-ion battery cell, subscript t express t At that moment, subscript max Indicates the upper limit value, subscript min Indicates the lower limit value; S3A2. Compare the voltage of the sodium-ion battery cell to be evaluated at the same moment with the set voltage value. If the voltage of the sodium-ion battery cell to be evaluated is higher than the set voltage value... U n,t,max or below U n,t,min If the voltage consistency of the sodium-ion battery cell to be evaluated does not meet the requirements, then the evaluation does not meet the requirements.

5. The method for online detection of battery performance consistency among sodium-lithium hybrid battery packs according to claim 1, characterized in that, The steps for determining the temperature consistency of lithium-ion cells in step S4 are as follows: S4A1. First, calculate the average temperature and standard deviation of all lithium-ion cells at the same time. Then, calculate the set temperature value using the average temperature and standard deviation. The set temperature value is [[...]]. T L,t,max , T L,t,min ],in, T L,t,max Indicates that lithium-ion cells are in t The upper limit of the temperature value set at any given time. T L,t,min Indicates that lithium-ion cells are in t The lower limit of the temperature value set at any time, subscript L Indicates lithium-ion battery cell, subscript t express t At that moment, subscript max Indicates the upper limit value, subscript min Indicates the lower limit value; S4A2. Compare the temperature of the lithium-ion cell to be evaluated at the same moment with the set temperature value. If the temperature of the lithium-ion cell to be evaluated is higher than the set temperature value... T L,t,max or below T L,t,min If the temperature consistency of the lithium-ion cell to be evaluated does not meet the requirements, then the evaluation does not meet the requirements.

6. The method for online detection of battery performance consistency among sodium-lithium hybrid battery packs according to claim 5, characterized in that, The formula for calculating the set temperature value is as follows: in, T L,t,avg This indicates that all lithium-ion cells in the vehicle are in t Average temperature at any given time; T L,t,std This indicates that all lithium-ion cells in the vehicle are in t The standard deviation of temperature at any given time.

7. The method for online detection of battery performance consistency among sodium-lithium hybrid battery packs according to claim 6, characterized in that, The steps for determining the voltage consistency of lithium-ion cells in step S4 are the same as those for determining the voltage consistency of sodium-ion cells in step S3.

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