Test method for sensitively and rapidly representing direct current internal resistance difference of battery cell
By using large-magnification to test the two extreme states and small-magnification to test the intermediate states in lithium-ion cell testing, the problems of long test time and unclear differences in the existing technology are solved, and a fast and sensitive DC internal resistance difference test is achieved. , reduces costs and is suitable for conventional ORT testing.
Patent Information
- Application Number
- CN202411138610.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-08-19
- Publication Date
- 2024-12-31
AI Technical Summary
The existing DC internal resistance difference test method for lithium-ion cells has a long test time and cannot clearly indicate the differences between cells, especially the test conditions under different SOC states.
The two extreme states are used to use large-magnification tests, and the intermediate state is used to use small-magnification tests. By gradually reducing the charge amount of the intermediate state, the test time is shortened and the intermediate state is reduced. After discharge, it is directly charged back to the original state, and multiple SOC states are used for testing.
It greatly shortens the test time, improves the sensitivity and accuracy of cell differences, reduces costs, and is suitable for conventional ORT testing.
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Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of ternary lithium-ion battery cells, and in particular relates to a testing method for sensitively and rapidly characterizing differences in direct current internal resistance of battery cells. Background Art
[0002] The DC internal resistance (DCIR) result is one of the important electrical properties for evaluating lithium-ion batteries. It is mainly used to measure the consistency of the battery and the health of the battery. The DCIR result is affected by temperature, rate, test time and SOC status.
[0003] There are three main DCIR test methods commonly used at present: 1. Discharge at a fixed rate for a period of time, and only measure the discharge DC internal resistance; 2. Pulse discharge-rest-charge at a fixed rate, and measure the discharge / charge DC internal resistance at different SOC states; 3. Continuously measure the DC internal resistance under dynamic voltage with alternating large and small currents. The existing test method tests the DCIR value under different SOC states by reducing the capacity by 10% from 100% capacity in sequence to obtain the DCIR result under the full state of 100%-0%. The test time is relatively long, about 46 hours; and the DCIR test under each SOC state uses the same rate method for charging and discharging, and the conditions are single, which cannot clearly show the differences between the cells. Summary of the invention
[0004] The present invention provides a test method for sensitively and quickly characterizing the difference in DC internal resistance of battery cells, reducing the intermediate states of the test, using a high rate test for the two extreme states, using a small rate test for the intermediate state, and directly charging back to the original state after the intermediate state discharge test, thereby solving the deficiencies described in the prior art.
[0005] The technical solution adopted by the present invention is: A test method for sensitively and quickly characterizing the difference in DC internal resistance of a battery cell, wherein the fully charged state is the first extreme state, the uncharged state is the second extreme state, an intermediate state is provided between the first extreme state and the second extreme state, and the charge amount in the intermediate state gradually decreases; the number of intermediate states is 2-7; At a set test temperature, the battery in the first extreme state is discharged using a first discharge rate, the discharge time is t, and the rest time after discharge is T1; The switching from the first extreme state to the intermediate state, from the current intermediate state to the next intermediate state, and from the intermediate state to the second extreme state is achieved by discharging at the second discharge rate, the discharge time at the second discharge rate is t, and the standing time after discharging at the second discharge rate is T; Each battery in the intermediate state is first discharged at the third discharge rate, and then left to stand after discharge, with the discharge time being t and the standing time being T; The discharged battery is charged back to the original intermediate state using the first charging rate, the charging time is t, the rest time is T1, the first charging rate is the same as the third discharge rate, and the second discharge rate is less than the third discharge rate and less than the first discharge rate; The battery in the second extreme state is charged at a second charge rate, the charging time is t, the rest time is T1, and the second charge rate is the same as the first discharge rate; The calculation formula of DC internal resistance in each SOC state is: DCIR = (initial voltage of SOC state - voltage of the last 1s of discharge / charge) / I 实际电流 .
[0006] The two extreme states are tested at a high rate, and the intermediate state is tested at a small rate to obtain the DCIR results of 100%-0 in the full state. Due to the reduction of the intermediate state and the use of different rates, the entire test time is greatly shortened, and the differences between the battery cells can be more sensitively characterized.
[0007] As a preferred solution of the present invention, a capacity test is first performed on the battery in the first extreme state before discharge, and the fully charged state after the capacity test is used as the first extreme state to ensure the accuracy of subsequent battery tests.
[0008] As a preferred solution of the present invention, there are three intermediate states, namely the first intermediate state, the second intermediate state and the third intermediate state.
[0009] As a preferred solution of the present invention, the first intermediate state is a 90% SOC state, the second intermediate state is a 50% SOC state, and the third intermediate state is a 10% SOC state.
[0010] As a preferred solution of the present invention, starting from the first extreme state, the battery is adjusted to the first intermediate state using the second discharge rate and left to stand for a standing time of T; The battery in the first intermediate state is discharged at a third discharge rate, and then allowed to stand after discharge, wherein the discharge time is t and the standing time is T; The discharged battery is charged back to the first intermediate state using the first charging rate, the charging time is t, the rest time is T1, and the first charging rate is the same as the third discharging rate; Using a second discharge rate, the battery in the first intermediate state is adjusted to a second intermediate state and allowed to stand for a period of time T; The battery in the second intermediate state is discharged at a third discharge rate, and then allowed to stand after discharge, wherein the discharge time is t and the standing time is T; The discharged battery is charged back to the second intermediate state using the first charging rate, the charging time is t, and the rest time is T1; Using the second discharge rate, the battery in the second intermediate state is adjusted to the third intermediate state and allowed to stand for a period of time T; The battery in the third intermediate state is discharged at a third discharge rate, and then allowed to stand after discharge, wherein the discharge time is t and the standing time is T; The discharged battery is charged back to the third intermediate state using the first charging rate, the charging time is t, and the rest time is T1; The battery in the third intermediate state is adjusted to the second extreme state using the second discharge rate and left to stand for a period of time T; and t <T1<T。
[0011] As a preferred solution of the present invention, the first discharge rate is 1.5~3C; the second discharge rate is 0.2~1C; and the third discharge rate is 1~1.5C.
[0012] As a preferred embodiment of the present invention, the t is 30-60s; T1 is 5-10min; and T is 30-60min.
[0013] As a preferred solution of the present invention, the number of batteries tested each time is 6 to 10 PCS.
[0014] The present invention uses a large rate to test the two extreme states, and uses a small rate to perform charge and discharge tests in the intermediate state, so as to obtain the DCIR result in the full state of 100%-0. Due to the reduction of the intermediate state and the use of different rates, the entire test time is greatly shortened, the cost is reduced, and the differences between the battery cells can be more sensitively characterized. In addition, the test method is simple and can be used for conventional ORT testing. DETAILED DESCRIPTION
[0015] Example: A sensitive and rapid test method for characterizing the DC internal resistance difference of battery cells. A certain number of sample cells are selected, 6~10PCS is optimal.
[0016] First, the capacity of the battery cell to be tested is tested to ensure that the battery cell to be tested is in a fully charged state, and the fully charged state is the first extreme state, the no-charge state is the second extreme state, and an intermediate state is set between the first extreme state and the second extreme state, and the charge amount in the intermediate state gradually decreases; The testing process of capacity testing is: In the standard test environment of 25°C, charge at 0.5C constant current to the cut-off voltage, then charge at constant voltage to 0.01C current cut-off, and let stand for 5 minutes; 0.2C constant current discharge to cut-off voltage, let stand for 5 minutes; 0.5C constant current is charged to the cut-off voltage, and then constant voltage is charged to 0.01C current cut-off, and then left to stand for 30-60 minutes; in this embodiment, it is left to stand for 60 minutes; at this time, it is 100% SOC state, that is, the first extreme state, and the voltage at the last 1s of standing is the initial voltage of the first extreme state; After the capacity test, the battery in the first extreme state is discharged at 2C for 30-60s, discharged for 60s here, and left to stand for 5-10min (1s stepping), and used for 10min here; of course, the discharge rate here can also be 1.5C, 2.5C and 3C.
[0017] Starting from the first extreme state, 10% SOC is discharged at 0.2C and left to stand for 60 minutes; the discharge rate here can also be 0.3C, 0.4C, 0.45C, 0.5C, 0.7C, 0.8C, 0.9C or 1C, etc.; it is set according to needs, and the interval is between 0.2C-1C; at this time, it is 90% SOC state, that is, the first intermediate state; the voltage at the last 1s of standing is the initial voltage of the first intermediate state; For the battery in the first intermediate state, discharge it at 1C for 60S, let it stand for 60min, then charge it at 1C for 60s, and let it stand for 10min (1s stepping); the discharge rate and charge rate here can be 1~1.5C, that is to say, 1.2C, 1.3C, and 1.5C can also be used.
[0018] Continue to discharge 40% SOC at 0.2C to adjust the battery in the first intermediate state to the second intermediate state, i.e., 50% SOC state, and let it stand for 60 minutes; the voltage at the last 1 second of standing is the initial voltage of the second intermediate state; For the battery in the second intermediate state, discharge it at 1C for 60s, let it stand for 60min, then charge it at 1C for 60s, let it stand for 10min (1s stepping); Continue to discharge 40% SOC at 0.2C, adjust the battery in the second intermediate state to the third intermediate state, i.e. 10% SOC, and let it stand for 60 minutes; the voltage at the last 1 second of standing is the initial voltage of the third intermediate state; For the battery in the third intermediate state, discharge it at 1C for 60 seconds, let it stand for 60 minutes, then charge it at 1C for 60 seconds, let it stand for 10 minutes (1 second stepping); Discharge to the cut-off voltage with 0.2C, adjust the battery in the third intermediate state to the second extreme state, i.e., 0% SOC state, and let it stand for 60 minutes. The voltage in the last 1 second of standing is the initial voltage of the second extreme state.
[0019] For the battery in the second extreme state, discharge at 2C for 60 seconds and let it stand for 10 minutes (1 second stepping); The calculation formula for the DC internal resistance DCIR at each SOC state is: DCIR = (initial voltage of SOC state - voltage of the last 1s of discharge / charge) / I 实际电流 .
[0020] In order to unify the measurement, the above formula is corrected to: DCIR = (initial voltage of SOC state - voltage of the last 1s of discharge / charge) / I 实际电流 *1000mΩ.
[0021] The test method provided by the present invention is simple, can be used for conventional ORT tests, and saves nearly 24 hours of test time. The charging and discharging time and the standing time are kept synchronized, which reduces costs, and can also accurately and sensitively characterize the differences between battery cells.
[0022] The principle of the present invention is described below by taking two different examples as examples.
[0023] 1. Two different materials for battery cells Take two groups of batteries, A and B. The two groups differ only in battery materials, and select 6 batteries from each group, totaling 12 batteries (good consistency); The two groups of cells were tested using the existing conventional DCIR test method to obtain the 6PCS average values under different SOC states, as shown in Tables 1 and 2.
[0024] Then the same battery cell is tested again according to the new test method of the present invention to obtain the 6PCS average values under different SOC states, as shown in Table III.
[0025] Table 1: Average results of conventional discharge DCIR test method Table 2: Average results of conventional charging DCIR test method Table 3: Average results of the discharge / charge DCIR test method of the present invention From the comparison of the average results of different test methods in the above table, it can be seen that the DCIR test result of the present invention is increased by 0.5~1mΩ compared with the conventional one, and the test time is saved by about 24 hours.
[0026] 2. Different ACRs for cells made of the same material Take two groups of cells, A / B, with the same materials and different ACR, and select 6 cells from each group, totaling 12 cells (better consistency); The ACR of group A cells is 13mΩ, and the ACR of group B cells is 14.5mΩ, a difference of 1.5m ohms; The two groups of cells were tested using the existing conventional DCIR test method, and the 6PCS average values under different SOC states were obtained, as shown in Tables 4 and 5; The same battery cell was tested again according to the new test method of the present invention, and the 6PCS average values under different SOC states were obtained, as shown in Table VI.
[0027] Table 4: Average results of conventional discharge DCIR test method Table 5: Average results of conventional charging DCIR test method Table 6: Average results of the discharge / charge DCIR test method of the present invention By comparing the average results of different test methods in the above table, it can be seen that the DCIR test result of the present invention is increased by 0.5~1mΩ compared with the conventional one, and the test time is saved by about 24 hours.
[0028] In summary, the DCIR test method of the present invention can sensitively and accurately characterize the differences between different materials or process changes of battery cells, has a wide range of applications and a simple method, and saves time to achieve the effect of reducing costs.
[0029] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.
[0030] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.
Claims
1. A sensitive and rapid test method for characterizing the difference in DC internal resistance of a battery cell, characterized in that: The fully charged state is the first extreme state, the uncharged state is the second extreme state, and an intermediate state is provided between the first extreme state and the second extreme state, and the charge amount of the intermediate state gradually decreases; the number of the intermediate states is 2-7; At a set test temperature, the battery in the first extreme state is discharged using a first discharge rate, the discharge time is t, and the rest time after discharge is T1; The switching from the first extreme state to the intermediate state, from the current intermediate state to the next intermediate state, and from the intermediate state to the second extreme state is achieved by discharging at the second discharge rate, the discharge time at the second discharge rate is t, and the standing time after discharging at the second discharge rate is T; Each battery in the intermediate state is first discharged at the third discharge rate, and then left to stand after discharge, with the discharge time being t and the standing time being T; The discharged battery is charged back to the original intermediate state using the first charging rate, the charging time is t, the rest time is T1, the first charging rate is the same as the third discharge rate, and the second discharge rate is less than the third discharge rate and less than the first discharge rate; The battery in the second extreme state is charged at a second charge rate, the charging time is t, the rest time is T1, and the second charge rate is the same as the first discharge rate; The calculation formula of DC internal resistance in each SOC state is: DCIR = (initial voltage of SOC state - voltage of the last 1s of discharge / charge) / I 实际电流 .
2. The method for sensitively and rapidly characterizing the difference in DC internal resistance of a battery cell according to claim 1, characterized in that: For the battery in the first extreme state, a capacity test is performed before discharging, and the fully charged state after the capacity test is used as the first extreme state.
3. The method for sensitively and rapidly characterizing the difference in DC internal resistance of a battery cell according to claim 1 or 2, characterized in that: There are three intermediate states, namely the first intermediate state, the second intermediate state and the third intermediate state.
4. The method for sensitively and rapidly characterizing the difference in DC internal resistance of a battery cell according to claim 3, characterized in that: The first intermediate state is a 90% SOC state, the second intermediate state is a 50% SOC state, and the third intermediate state is a 10% SOC state.
5. The method for sensitively and rapidly characterizing the difference in DC internal resistance of a battery cell according to claim 4, characterized in that: Starting from the first extreme state, the battery is adjusted to the first intermediate state using the second discharge rate and left to stand for a standing time of T; The battery in the first intermediate state is discharged at a third discharge rate, and then allowed to stand after discharge, wherein the discharge time is t and the standing time is T; The discharged battery is charged back to the first intermediate state using the first charging rate, the charging time is t, the rest time is T1, and the first charging rate is the same as the third discharging rate; Using a second discharge rate, the battery in the first intermediate state is adjusted to a second intermediate state and allowed to stand for a period of time T; The battery in the second intermediate state is discharged at a third discharge rate, and then allowed to stand after discharge, wherein the discharge time is t and the standing time is T; The discharged battery is charged back to the second intermediate state using the first charging rate, the charging time is t, and the rest time is T1; Using the second discharge rate, the battery in the second intermediate state is adjusted to the third intermediate state and allowed to stand for a period of time T; The battery in the third intermediate state is discharged at a third discharge rate, and then allowed to stand after discharge, wherein the discharge time is t and the standing time is T; The discharged battery is charged back to the third intermediate state using the first charging rate, the charging time is t, and the rest time is T1; The battery in the third intermediate state is adjusted to the second extreme state using the second discharge rate and left to stand for a period of time T; and t <T1<T。 6. The method for sensitively and rapidly characterizing the difference in DC internal resistance of a battery cell according to claim 5, characterized in that: The first discharge rate is 1.5~3C; the second discharge rate is 0.2~1C; and the third discharge rate is 1~1.5C.
7. The method for sensitively and rapidly characterizing the difference in DC internal resistance of a battery cell according to claim 6, characterized in that: The t is 30-60s; T1 is 5-10min; and T is 30-60min.
8. The method for sensitively and rapidly characterizing the difference in DC internal resistance of a battery cell according to claim 7, characterized in that: The number of batteries tested each time is 6~10PCS.