Method for testing low-temperature capacity of battery

Abstract

The invention provides a battery low-temperature capacity testing method, and belongs to the technical field of secondary batteries. The test method can accurately test the capacity of the battery at low temperature; in addition, the test method has low requirements on test equipment, the application range is wide, the low-temperature capacity test process can be automatically carried out according to a preset test program, test personnel do not need to issue a test restart instruction, manpower is saved, and the test efficiency is relatively high.

Description

Technical Field

[0001] The invention belongs to the technical field of secondary batteries, and in particular relates to a method for testing the low-temperature capacity of a battery. Background Art

[0002] In recent years, lithium-ion batteries have been widely used in energy storage power stations, energy storage power supplies, power tools, electric bicycles, hybrid electric vehicles and pure electric vehicles, and have become one of the important ways to cope with the global energy crisis and environmental pressure.

[0003] Before using lithium-ion batteries, it is necessary to test the capacity of lithium-ion batteries. The test method is to place the battery under test in a test environment for charge and discharge test. Since the internal resistance of the battery under test will cause the temperature of the battery itself to rise during the charge and discharge process, and high temperature is conducive to the battery capacity. The greater the internal resistance of the battery, the higher the temperature rise, and the more battery capacity the lithium-ion battery exerts, resulting in a higher discharge capacity test result for the lithium-ion battery.

[0004] However, in actual applications, lithium-ion batteries need to be used at a constant temperature. Especially in the field of pure electric vehicles, many automobile manufacturers require the capacity of batteries at different constant temperatures as a performance reference indicator and a very important component of BMS logic application.

[0005] Patent application document CN116930777A discloses a battery low temperature capacity test method, device, electronic device and storage medium. The test method obtains the first temperature of the battery during the discharge test, compares the first preset temperature threshold with the first temperature, stops the battery discharge test if the first temperature is greater than the first preset temperature threshold, cools the battery, detects the second temperature during the battery cooling process, and continues the battery discharge test until the second temperature is less than or equal to the second preset temperature threshold, repeatedly obtains the first temperature of the battery during the discharge test until the second temperature is less than or equal to the second preset temperature threshold, continues the battery discharge test, and the battery voltage is equal to the second cut-off voltage, and the battery discharge capacity in all discharge tests is counted.

[0006] The above test method requires that the charge and discharge test equipment can be linked with the battery temperature, which places high demands on the test equipment. However, many test equipment can only alarm and pause when the battery temperature rises to a certain preset value. The temperature needs to be lowered before the tester can issue a test restart instruction. It is impossible to achieve the battery temperature drop to the ambient temperature to continue to start the discharge, so the scope of application of this test method is relatively small. And issuing a test restart instruction by the tester will seriously waste manpower, and the test time may increase due to untimely restart, which will reduce the test efficiency. Summary of the invention

[0007] The present invention aims to solve at least one of the technical problems in the related art to some extent. For this purpose, an embodiment of the present invention provides a method for testing the low-temperature capacity of a battery. This testing method can accurately test the capacity of the battery at low temperature; in addition, this testing method has low requirements for testing equipment, a wide range of applications, and does not require testers to issue a test restart instruction during the low-temperature capacity testing process, saving manpower and having a relatively high testing efficiency.

[0008] An embodiment of the present invention provides a method for testing the low-temperature capacity of a battery, including the following steps:

[0009] S1. Provide a finished battery cell;

[0010] S2. Perform an uncontrolled low-temperature capacity test on the finished battery cell at the target test temperature T2, with a constant current discharge rate of n1 and a cut-off voltage of V1, to obtain a battery temperature T - time t curve;

[0011] S3. According to the temperature control requirements for the low-temperature capacity test of the battery, with a temperature rise ≤ T1, find the time t1 corresponding to the temperature rise T1 in the battery temperature T - time t curve;

[0012] S4. (1) Perform an uncontrolled normal-temperature capacity test on the finished battery cell at normal temperature to obtain the nominal capacity C0 of the battery;

[0013] (2) Change the temperature to the target test temperature T2 and set aside for at least 10 h;

[0014] (3) Perform a temperature-controlled low-temperature capacity test on the finished battery cell at the target test temperature T2, with a constant current discharge of n1×C0 for X×t1 time, to obtain a discharge capacity of Cn; where 0 < X < 1;

[0015] (4) Set aside for at least 50 min;

[0016] (5) Preset the cycles of steps (3) and (4) to N weeks, where 1 ≤ N;

[0017] (6) The cut-off voltage for step (3) of the cycle is V1, and the actual number of cycles is n weeks, where n < N; accumulate the sum of the discharge capacities of step (3) of the cycle C = C1 + C2 + … C n is the discharge capacity of the battery under temperature control at the target test temperature T2.

[0018] The advantages and technical effects brought by the testing method of the embodiment of the present invention are as follows:

[0019] (1) The test method can be applied to all battery systems including lithium iron phosphate, lithium iron manganese phosphate, ternary materials, and all packaging modes such as soft pack, aluminum shell, and cylinder to accurately test the capacity of the battery at low temperature. This is conducive to the test of the actual capacity of the battery at low temperature, making the calibration of the BMS of new energy vehicles more accurate, and avoiding the inaccurate endurance estimation and sudden breakdown caused by incorrect capacity calibration.

[0020] (2) The test method has low requirements on the test equipment and has a wide range of applications. In addition, the low-temperature capacity test can be automatically performed according to a preset test program, without the need for the tester to issue a test restart instruction, thus saving manpower and increasing the test efficiency.

[0021] In some embodiments, T2≤0°C.

[0022] In some embodiments, -50°C ≤ T2 ≤ 0°C.

[0023] In some embodiments, 0°C <T1。

[0024] In some embodiments, 0°C <T1≤8℃。

[0025] In some embodiments, in step (2), the step is left to stand for 10 to 24 hours.

[0026] In some embodiments, in step (4), the mixture is left to stand for 50 to 100 minutes.

[0027] In some embodiments, it is characterized in that 20 <N。 BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is the battery temperature T-time t curve obtained by the low-temperature capacity test without temperature control in Example 1. DETAILED DESCRIPTION

[0029] Embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0030] An embodiment of the present invention provides a method for testing the low temperature capacity of a battery, comprising the following steps:

[0031] S1. Provide finished battery cells;

[0032] S2. Perform an uncontrolled low-temperature capacity test on the finished battery cell at the target test temperature T2, with a constant current discharge rate of n1 and a cut-off voltage of V1, to obtain a battery temperature T-time t curve;

[0033] S3. According to the temperature control requirements for the low-temperature capacity test of the battery, the temperature rise ≤ T1, and find the time t1 corresponding to the temperature rise T1 in the battery temperature T - time t curve;

[0034] S4. (1) Conduct an uncontrolled room-temperature capacity test on the finished battery cells at room temperature to obtain the nominal battery capacity C0;

[0035] (2) Change the temperature to the target test temperature T2 and set aside for at least 10 h;

[0036] (3) Conduct a temperature-controlled low-temperature capacity test on the finished battery cells at the target test temperature T2, discharge at a constant current of n1×C0 for X×t1 hours, and obtain the discharge capacity Cn; where 0 < X < 1;

[0037] (4) Set aside for at least 50 min;

[0038] (5) Preset the cycles of steps (3) and (4) to N weeks, where 1 ≤ N;

[0039] (6) The cut-off voltage for step (3) is V1, and the actual number of cycles is n weeks, where n < N; accumulate the sum of the discharge capacities of step (3) C = C1 + C2 + … C n is the discharge capacity of the battery at the target test temperature T2 under temperature control.

[0040] In the test method of the embodiment of the present invention, in step (3), the constant-current discharge time is X×t1, and 0 < X < 1. Setting this condition is to control the temperature rise during the test in step (3) not to exceed T1. Setting aside for at least 50 min in step (4) is to allow the battery cells with a slightly increased temperature during the test in step (3) to cool down to the target test temperature T2 again, so as to make the low-temperature capacity test result more accurate.

[0041] In addition, it should be noted that the N weeks in step (5) is the preset number of cycles for the test equipment, which is estimated based on the nominal battery capacity C0, and N needs to be greater than the actual number of cycles n.

[0042] In addition, it can be understood that when discharging at a constant current of n1×C0 for X×t1 hours in step (3) to obtain the discharge capacity C1, discharging at a constant current of n1×C0 for X×t1 hours to obtain the discharge capacity C2, discharging at a constant current of n1×C0 for X×t1 hours to obtain the discharge capacity C3, and so on, discharging at a constant current of n1×C0 for X×t1 hours to obtain the discharge capacity C n . In step (6), cut off with the protection voltage V1 to obtain the actual number of cycles n, and then accumulate the sum of the discharge capacities of step (3) C = C1 + C2 + … C n is the discharge capacity of the battery at the target test temperature T2 under temperature control.

[0043] In some embodiments, T2 ≤ 0 °C. In some embodiments, -50 °C ≤ T2 ≤ 0 °C, such as -50 °C, -40 °C, -30 °C, -20 °C, -10 °C, 0 °C, etc. The specific value of the target test temperature T2 needs to be customized according to the requirements of battery application manufacturers. The test method of the embodiments of the present invention can be applied to the above test temperatures, and the test results are all very accurate.

[0044] In some embodiments, 0 °C < T1. In some embodiments, 0 °C < T1 ≤ 8 °C, such as 0.5 °C, 1 °C, 2 °C, 3 °C, 4 °C, 5 °C, 6 °C, 7 °C, 8 °C, etc. The specific value of the temperature rise T1 needs to be customized according to the requirements of battery application manufacturers. The test method of the embodiments of the present invention can be applied to the above temperature rises, and the test results are all very accurate.

[0045] In some embodiments, in step (2), it is left to stand for 10 to 24 h, such as 10 h, 12 h, 14 h, 16 h, 18 h, 20 h, 22 h, 24 h, etc. Standing for the above time is to reduce the temperature of the finished battery cell to the target test temperature T2.

[0046] In some embodiments, in step (4), it is left to stand for 50 to 100 min, such as 50 min, 60 min, 70 min, 80 min, 90 min, 100 min. Standing for the above time can make the temperature of the finished battery cell that has slightly increased during the test in step (3) drop back to the target test temperature T2 again, so as to make the low-temperature capacity test result more accurate.

[0047] In some embodiments, it is characterized in that 20 < N, such as 20, 25, 30, 35, 40, 45, 50, etc. N is estimated from the nominal capacity C0 of the battery. N can be set to the above values, so that a relatively loose margin can be reserved relative to n, and then it is ensured that N can be greater than the actual number of cycles n, so as to ensure that the test program can be automatically carried out and avoid the situation of manual start.

[0048] The present invention will be described in detail below with reference to embodiments and drawings.

[0049] Embodiment 1

[0050] This embodiment provides a -30 °C low-temperature capacity test method with a temperature control of ±5 °C, and the battery cell is a 100 Ah lithium iron phosphate square aluminum shell battery cell. In the process of manufacturing the aluminum shell battery, other processes such as mixing, coating, rolling, winding / stacking, liquid injection, and high-temperature aging are carried out normally, which are exactly the same as those of normal battery cells.

[0051] 1. Perform an uncontrolled low-temperature capacity test on the finished battery cell at the target test temperature of -30 °C, with a constant current discharge rate of n1 = 1 / 3C and a cut-off voltage of 2.0V. Obtain as Figure 1The battery temperature T-time t curve is shown.

[0052] 2. According to the temperature control requirements of the battery low temperature capacity test, the temperature rise is ≤5°C. In the battery temperature T~time t curve, find the time t1=720s corresponding to the temperature rise of 5°C.

[0053] 3. Set the cycle steps according to the above parameters

[0054] 1) The test environment temperature is 25±2℃;

[0055] 2) Place at 25±2℃ for 5h;

[0056] 3) Discharge at 1.0C constant current to 2.5V (the normal temperature working voltage range of lithium iron phosphate battery is generally 2.5~3.65V), and the protection time is 1.5h;

[0057] 4) Leave for 60 minutes;

[0058] 5) 1.0C constant current and constant voltage charging to 3.65V (the operating voltage range of lithium iron phosphate battery at room temperature is generally 2.5~3.65V), the cut-off current is 0.05C, and the protection time is 1.5h;

[0059] 6) Leave for 60 minutes;

[0060] 7) Discharge at 1.0C constant current to 2.5V, protection time is 1.5h;

[0061] 8) Leave for 60 minutes;

[0062] 9) Cycle steps 5) to 8) for 3 cycles and record the nominal capacity C0 = 101.7 Ah;

[0063] 10) Leave for 60 minutes;

[0064] 10) Change the temperature to the target test temperature -30°C;

[0065] 10) Set aside for 12 hours;

[0066] 11)n1×C0 constant current discharge X×t1 min, the discharge capacity is C n ;

[0067] 12) Set aside for 60 minutes;

[0068] 13) Preset the cycle of steps 11) and 12) to N = 30 cycles;

[0069] 14) The protection voltage stops after 2.0V is cut off. The actual number of cycles is n = 12 cycles. 12As shown in Table 1, the cumulative cycle 11) step discharge capacity sum C = C1 + C2 + C3 + C4 + C5 + C6 + C7 + C8 + C9 + C 10 +C 11 +C 12 =38.56Ah is the discharge capacity of the battery under temperature control.

[0070] Table 1. Cycle 11) step discharge capacity

[0071] <![CDATA[C1]]> 3.39Ah <![CDATA[C2]]> 3.39Ah <![CDATA[C3]]> 3.39Ah <![CDATA[C4]]> 3.39Ah <![CDATA[C5]]> 3.39Ah <![CDATA[C6]]> 3.39Ah <![CDATA[C7]]> 3.39Ah <![CDATA[C8]]> 3.39Ah <![CDATA[C9]]> 3.39Ah <![CDATA[C 10 ]]> 3.39Ah <![CDATA[C 11 ]]> 3.39Ah <![CDATA[C 12 ]]> 1.27Ah

[0072] Comparative Example 1

[0073] This embodiment provides a -30°C low temperature capacity test method without temperature control, and the battery cell is a 100Ah lithium iron phosphate square aluminum shell battery cell. The aluminum shell battery sample preparation process is normally carried out, and other processes such as mixing, coating, rolling, winding / lamination, liquid injection, high temperature aging, etc. are exactly the same as normal batteries.

[0074] 1) The test environment temperature is 25±2℃;

[0075] 2) Place at 25±2℃ for 5h;

[0076] 3) Discharge at 1.0C constant current to 2.5V, protection time is 1.5h;

[0077] 4) Leave for 60 minutes;

[0078] 5) 1.0C constant current and constant voltage charging to 3.65V, cut-off current is 0.05C, protection time is 1.5h;

[0079] 6) Leave for 60 minutes;

[0080] 7) Discharge at 1.0C constant current to 2.5V, protection time is 1.5h;

[0081] 8) Leave for 60 minutes;

[0082] 9) Cycle steps 5) to 8) for 3 cycles and record the nominal capacity C0 = 101.7 Ah;

[0083] 10) Leave for 60 minutes;

[0084] 10) Change the temperature to the target test temperature -30°C;

[0085] 10) Set aside for 12 hours;

[0086] 11) 1 / 3C0 constant current discharge, protection voltage 2.0V cut-off, discharge capacity C = 53.29Ah;

[0087] 12) Set aside for 60 minutes;

[0088] C=53.29Ah, and the test temperature rise is 20.2° C. Due to the large temperature rise, the discharge capacity of 53.29Ah measured in this comparative example is significantly different from the actual discharge capacity of 38.56Ah at -30° C. in Example 1.

[0089] In the present invention, the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" etc. mean 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 representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the described specific features, structures, materials or characteristics may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0090] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A method for testing the low temperature capacity of a battery, characterized in that: The following steps are involved: S1. Provide finished battery cells; S2. Perform an uncontrolled low-temperature capacity test on the finished battery cell at the target test temperature T2, with a constant current discharge rate of n1 and a cut-off voltage of V1, to obtain a battery temperature T-time t curve; S3. According to the temperature control requirements of the battery low temperature capacity test, the temperature rise is ≤ T1, and the time t1 corresponding to the temperature rise T1 is found in the battery temperature T~time t curve; S4. (1) performing a capacity test of the finished battery cell at room temperature without temperature control to obtain the nominal capacity of the battery C0; (2) Change the temperature to the target test temperature T2 and leave it for at least 10 hours; (3) performing a temperature-controlled low-temperature capacity test on the finished battery cell at a target test temperature T2, discharging at a constant current of n1×C0 for a time of X×t1, and obtaining a discharge capacity of Cn; Where 0<X<1; (4) Leave for at least 50 minutes; (5) Preset the cycle of steps (3) and (4) to N cycles, where 1 ≤ N; (6) The cut-off voltage of step (3) is V1, and the actual number of cycles is n, where n <N; The sum of the discharge capacities of the cumulative cycle (3) step is C = C1 + C2 + ... C n It is the discharge capacity of the battery under temperature control at the target test temperature T2.

2. The testing method according to claim 1, characterized in that: T2≤0℃。 3. The testing method according to claim 2, characterized in that: -50℃≤T2≤0℃。 4. The testing method according to claim 1, characterized in that: 0℃<T1。 5. The testing method according to claim 1, characterized in that: 0℃<T1≤8℃。 6. The testing method according to claim 1, characterized in that: In step (2), leave it aside for 10 to 24 hours.

7. The testing method according to claim 1, characterized in that: In step (4), let stand for 50 to 100 minutes.

8. The testing method according to claim 1, characterized in that: 20<N。

Images