Lithium battery sorting method

Abstract

The invention relates to a lithium battery technology, and provides a lithium battery sorting method which comprises the following steps: carrying out basic function test on lithium batteries; if the basic function of the lithium battery is normal, performing direct-current internal resistance test, capacity test and voltage drop rate test on the lithium battery in sequence to obtain a direct-current internal resistance test value, a capacity test value and a voltage drop rate test value of the lithium battery; and sorting the lithium batteries according to the DC internal resistance test value, the capacity test value and the voltage drop rate test value. According to the invention, the lithium battery sorting consistency can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and more particularly to a method for sorting lithium batteries. Background Art

[0002] Lithium-ion batteries have the advantages of wide temperature tolerance, long cycle life, high rate performance, and high safety, and are widely used in fields such as consumer electronics, electric vehicles, and energy storage systems.

[0003] Sorting of lithium batteries is a key step to ensure battery performance consistency, improve safety, extend service life, and optimize resource utilization. Whether in production, application, or recycling, sorting can significantly improve the economic efficiency and environmental friendliness of lithium batteries.

[0004] How to improve the consistency of lithium battery sorting is a technical problem that needs to be solved urgently by those skilled in the art. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for sorting lithium batteries, which can improve the consistency of lithium battery sorting.

[0006] The embodiments of the present invention can be implemented as follows:

[0007] In a first aspect, the present invention provides a method for sorting lithium batteries, the method comprising:

[0008] Performing a basic function test on the lithium battery;

[0009] If the basic function of the lithium battery is normal, then sequentially performing a DC internal resistance test, a capacity test, and a voltage drop rate test on the lithium battery to obtain a DC internal resistance test value, a capacity test value, and a voltage drop rate test value of the lithium battery;

[0010] Sorting the lithium battery according to the DC internal resistance test value, the capacity test value, and the voltage drop rate test value.

[0011] In an alternative embodiment, the step of performing a basic function test on the lithium battery comprises:

[0012] Charging and discharging the lithium battery with a first current to obtain a function test result;

[0013] The step of if the basic function of the lithium battery is normal, then sequentially performing a DC internal resistance test, a capacity test, and a voltage drop rate test on the lithium battery to obtain a DC internal resistance test value, a capacity test value, and a voltage drop rate test value of the lithium battery comprises:

[0014] If the functional test result indicates that the basic functions of the lithium battery are normal, then charge and discharge the lithium battery with a second current to obtain a DC internal resistance test value of the lithium battery, where the second current is greater than the first current;

[0015] Charge and discharge the lithium battery with a third current to obtain a capacity test value of the lithium battery, where the third current is less than the second current;

[0016] Charge and discharge the lithium battery with a fourth current to obtain a voltage drop rate test value of the lithium battery.

[0017] In an alternative embodiment, the step of charging and discharging the lithium battery with the first current to obtain a functional test result includes:

[0018] Discharge the lithium battery at a constant current with the first current until the constant current discharge duration reaches a first discharge duration or the voltage of the lithium battery reaches a first preset cut-off voltage, where the first preset cut-off voltage is the voltage of the lithium battery when the remaining power of the lithium battery is a first preset proportion of the total power;

[0019] Keep the voltage of the lithium battery at the first preset cut-off voltage and perform a constant voltage discharge until the constant voltage discharge duration reaches a second discharge duration or the current of the lithium battery is less than a preset cut-off current;

[0020] Let the lithium battery after the constant voltage discharge stand for a first preset standing duration;

[0021] Charge the lithium battery at a constant current with the first current after the lithium battery has stood for the first preset standing duration;

[0022] When the lithium battery reaches a preset protection voltage, if the constant current charging stops, then obtain the functional test result indicating that the basic functions of the lithium battery are normal, otherwise obtain the functional test result indicating that the basic functions of the lithium battery are abnormal.

[0023] In an alternative embodiment, the step of, if the functional test result indicates that the basic functions of the lithium battery are normal, then charge and discharge the lithium battery with a second current to obtain a DC internal resistance test value of the lithium battery includes:

[0024] Discharge the lithium battery at a constant current with the second current until the discharge duration reaches a preset cut-off duration to obtain a discharge DC internal resistance of the lithium battery;

[0025] Let the lithium battery after the constant current discharge stand for a second preset standing duration;

[0026] With the second current, perform constant current charging on the lithium battery after it has been static for the second preset static duration until the charging duration reaches the preset cut-off duration, to obtain the charging DC internal resistance of the lithium battery, and finally obtain the DC internal resistance test value including the discharge DC internal resistance and the charging DC internal resistance.

[0027] In an alternative embodiment, before the step of performing constant current discharge on the lithium battery with the second current until the discharge duration reaches the preset cut-off duration to obtain the discharge DC internal resistance of the lithium battery, it includes:

[0028] Discharge the lithium battery with a preset current such that the voltage of the lithium battery after discharge reaches a first preset cut-off voltage, where the first preset cut-off voltage is the voltage of the lithium battery when the remaining power of the lithium battery is at a first preset proportion of the total power;

[0029] Let the lithium battery with the voltage reaching the first preset cut-off voltage be static for the first preset static duration.

[0030] In an alternative embodiment, the step of performing charge and discharge on the lithium battery with the third current to obtain the capacity test value of the lithium battery includes:

[0031] Perform constant current charging on the lithium battery with the third current until the voltage of the lithium battery reaches a first preset stable voltage;

[0032] Let the lithium battery with the voltage reaching the first preset stable voltage be static for the first preset static duration;

[0033] Perform constant current discharge on the lithium battery after being static for the first preset static duration with the third current until the voltage of the lithium battery reaches a second preset stable voltage, obtain the discharge amount of the constant current discharge and use the discharge amount as the capacity test value.

[0034] In an alternative embodiment, the step of performing charge and discharge on the lithium battery with the fourth current to obtain the voltage drop rate test value of the lithium battery includes:

[0035] Perform constant current charging on the lithium battery with the fourth current until the voltage of the lithium battery reaches a second preset cut-off voltage, where the second preset cut-off voltage is the voltage of the lithium battery when the remaining power of the lithium battery is at a second preset proportion of the total power;

[0036] Keep the voltage of the lithium battery at the second preset cut-off voltage and perform constant voltage charging until the constant voltage charging duration reaches the preset charging duration or the current of the lithium battery is less than the preset cut-off current and obtain the first voltage of the lithium battery at this time;

[0037] After the lithium battery after constant voltage charging is left standing for a third preset standing duration, obtain the second voltage of the lithium battery at this time;

[0038] According to the first voltage, the second voltage and the third preset standing duration, calculate the voltage drop rate test value.

[0039] In an alternative embodiment, before the step of continuing to charge and discharge the lithium battery, it includes:

[0040] Leave the lithium battery standing for a preset duration.

[0041] In an alternative embodiment, the first current is less than or equal to 1C, the second current is greater than or equal to 2C, the third current is 1C, and the fourth current is less than or equal to 1C.

[0042] In an alternative embodiment, there are multiple lithium batteries, and the step of sorting the lithium batteries according to the DC internal resistance test value, the capacity test value and the voltage drop rate test value includes:

[0043] Group the multiple lithium batteries according to the capacity test value to obtain at least one first group;

[0044] Continue to group the lithium batteries in each first group according to the DC internal resistance test value to obtain at least one second group;

[0045] Continue to group the lithium batteries in each second group according to the voltage drop rate test value to obtain at least one third group;

[0046] Take all the third groups as the sorting result of sorting the multiple lithium batteries.

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] In this embodiment, during the continuous test process, the DC internal resistance test value, the capacity test value and the voltage drop rate test value of the lithium battery are obtained in sequence to sort the lithium battery. Since the target lithium battery is sorted and evaluated from various index dimensions such as the function, DC internal resistance, capacity, and voltage drop rate of the target lithium battery, the final sorting consistency can be ensured. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the embodiments. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0050] Figure 1 The flowchart example of the lithium battery sorting method provided in this embodiment Figure 1 。

[0051] Figure 2 The flowchart example of the lithium battery sorting method provided in this embodiment Figure 2 。

[0052] Figure 3 The flowchart example of the lithium battery sorting method provided in this embodiment Figure 3 。

[0053] Figure 4 The example diagram of the lithium battery sorting process provided in this embodiment. Detailed implementation manners

[0054] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some but not all of the embodiments of the present invention. Usually, the components of the embodiments of the present invention described and illustrated in the accompanying drawings here can be arranged and designed in various different configurations.

[0055] Therefore, the detailed description of the embodiments of the present invention provided in the accompanying drawings below is not intended to limit the scope of the claimed present invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0056] It should be noted that: similar reference numerals and letters denote similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0057] In the description of the present invention, it should be noted that if terms such as "upper", "lower", "inner", "outer", etc. are used to indicate the orientation or positional relationship, it is based on the orientation or positional relationship shown in the accompanying drawings or the orientation or positional relationship in which the product of this invention is usually placed during use. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be construed as a limitation of the present invention.

[0058] In addition, if terms such as "first", "second", etc. are used only for distinguishing descriptions, they cannot be understood as indicating or implying relative importance.

[0059] It should be noted that the features in the embodiments of the present invention can be combined with each other without conflict.

[0060] Please refer to Figure 1 , Figure 1 which is a process example of the lithium battery sorting method provided in this embodiment Figure 1 , and this method includes the following steps:

[0061] Step S101, perform basic function tests on the lithium battery;

[0062] In this embodiment, lithium batteries include, but are not limited to, lithium titanate batteries, lithium iron phosphate batteries, lithium polymer batteries, lithium manganese oxide batteries, etc. The basic function tests include detecting whether the module channels in the lithium battery are normal, such as whether the charging channel and the discharging channel are normal, and whether the channel connectivity between the components inside the lithium battery is normal, etc. Only on the premise of normal basic functions does it make sense to continue with other tests.

[0063] It can be understood that before performing basic function tests on the lithium battery, it is also necessary to prepare the charged lithium battery to be tested and the test environment. For example, perform a preliminary screening on the lithium battery to be tested, screen the sealed lithium batteries for testing, or screen the lithium batteries produced in a preset batch, and control the temperature or humidity of the test environment, etc.

[0064] Step S102, if the basic functions of the lithium battery are normal, then perform a direct current internal resistance test, a capacity test, and a voltage drop rate test on the lithium battery in sequence to obtain the direct current internal resistance test value, the capacity test value, and the voltage drop rate test value of the lithium battery.

[0065] In this embodiment, the direct current internal resistance is abbreviated as DC Internal Resistance or DCIR or DCR. The direct current internal resistance is used to evaluate the health status of the lithium battery. For example, the direct current internal resistance of an aging lithium battery will increase. The capacity determines the battery life of the lithium battery, and the voltage drop rate is used to evaluate the performance of the lithium battery under high-rate discharge, which helps to optimize the low-voltage protection strategy of the lithium battery.

[0066] In this embodiment, the direct current internal resistance, the capacity, and the voltage drop rate are not isolated from each other, but there is a certain influence relationship: the direct current internal resistance directly affects the voltage drop rate: the greater the direct current internal resistance, the faster the voltage drops during discharge. The capacity determines the battery life of the lithium battery, but the effective capacity will be reduced due to the influence of the direct current internal resistance and the voltage drop rate during high-rate discharge: the voltage drop rate is a comprehensive manifestation of the performance of the lithium battery and is jointly affected by the direct current internal resistance and the capacity. And this embodiment is exactly based on the influence relationship among the three, and performs a direct current internal resistance test, a capacity test, and a voltage drop rate test on the lithium battery in sequence, which can not only ensure the comprehensiveness of the test, but also ensure the consistency of these three test values, and finally achieve the consistency of lithium battery sorting.

[0067] Step S103: Sort the lithium batteries according to the DC internal resistance test value, the capacity test value, and the voltage drop rate test value.

[0068] In this embodiment, sorting the lithium batteries means grouping and classifying multiple lithium batteries according to the DC internal resistance test value, the capacity test value, and the voltage drop rate test value, ensuring the consistency of the three indicators of DC internal resistance, capacity, and voltage drop rate in the grouping and classification, so as to improve the service life of the lithium batteries in the same group.

[0069] The above method provided in this embodiment sorts the lithium batteries by obtaining the DC internal resistance test value, the capacity test value, and the voltage drop rate test value of the lithium batteries in sequence during the continuous test process. Since the sorting and evaluation of the target lithium batteries are carried out from various index dimensions such as the function, DC internal resistance, capacity, and voltage drop rate of the target lithium batteries, the final sorting consistency can be ensured.

[0070] Due to the magnitude of the curing current, it is easy to keep the lithium battery in the same state for a long time, resulting in acquisition distortion and memory effect of module components, affecting the accuracy and effectiveness of the test results. To solve this problem, in this embodiment, during the continuous test process, on the premise of meeting the test requirements, the "memory fatigue" caused by the curing current is avoided by changing the current, improving the accuracy and effectiveness of the test results. This embodiment is based on Figure 1 Another lithium battery sorting method is provided. Please refer to Figure 2 , Figure 2 is a flow example of the lithium battery sorting method provided in this embodiment Figure 2 Step S101 includes the following sub-steps:

[0071] Sub-step S1010: Charge and discharge the lithium battery with a first current to obtain the function test result.

[0072] In this embodiment, since only the basic functions are being tested, the first current can be a current less than or equal to 1C. The 1C current refers to the charge and discharge rate of a lithium battery, expressed as a multiple of the rated capacity of the lithium battery. C (Capacity) is the rated capacity of the lithium battery, usually measured in ampere-hours (Ah). Therefore, a 1C current means charging and discharging at the rate of the rated capacity of the lithium battery. For charging, if the rated capacity of a lithium battery is 10Ah, then the charging rate of a 1C current is 10A, meaning the lithium battery can be fully charged within 1 hour. Similarly, for discharging, if the rated capacity of a lithium battery is 10Ah, then the discharging rate of a 1C current is 10A. This means that the battery's charge will be completely depleted within 1 hour. In addition to the 1C current, there are other charge and discharge rates, such as a 0.5C current or a 2C current. For a 0.5C current, it means charging and discharging at half the current of the rated capacity of the lithium battery. For a 2Ah lithium battery, the 0.5C charging rate is 1A. For a 2C current, it means charging and discharging at twice the current of the rated capacity of the lithium battery. For a 2Ah lithium battery, the 2C charging rate is 4A.

[0073] In this embodiment, in order to cover the comprehensiveness of the basic functions, be able to test both constant current and constant voltage, and smoothly proceed with the next test, this embodiment provides an implementation method of first constant current discharging, then constant voltage discharging, and then constant current charging:

[0074] First, discharge the lithium battery at a constant current with the first current until the constant current discharge duration reaches the first discharge duration or the voltage of the lithium battery reaches the first preset cut-off voltage. The first preset cut-off voltage is the voltage of the lithium battery when the remaining power of the lithium battery is at the first preset proportion of the total power.

[0075] In this embodiment, the first discharge duration can be set according to the actual parameters of the lithium battery. For example, the first discharge duration is 30 minutes. The first preset proportion can be 50%. At this time, the first preset cut-off voltage can be the voltage of the lithium battery when the remaining power of the lithium battery is 50% of the total power. The first preset cut-off voltage can also be expressed as 50% SOC. SOC (State of Charge) refers to the state of charge of the battery, which is an index to measure the current remaining power of the battery, usually expressed in percentage. The range of SOC is usually from 0% to 100%, where 0% means the battery is fully discharged and 100% means the battery is fully charged.

[0076] Secondly, keep the voltage of the lithium battery at the first preset cut-off voltage and perform constant voltage discharging until the constant voltage discharge duration reaches the second discharge duration or the current of the lithium battery is less than the preset cut-off current.

[0077] In this embodiment, the second discharge duration can be set according to the parameters of the lithium battery. For example, the second discharge duration is 15 minutes, and the preset cut-off current can be the relatively stable current reached by the lithium battery during the constant voltage charge and discharge process of the lithium battery. For example, the preset cut-off current is 0.1C.

[0078] Third, let the lithium battery after constant voltage discharge stand for the first preset standing duration;

[0079] In this embodiment, the purpose of letting the lithium battery stand is as follows: (1) During the charge and discharge process of the lithium battery, some by-products such as gases or crystalline substances will be generated due to internal chemical reactions. Standing can allow these by-products to gradually precipitate or dissolve, thereby reducing the negative impact on battery performance. At the same time, standing helps the electrochemical reaction between the electrode material and the electrolyte to tend to balance, ensuring the accuracy of subsequent test data; (2) After charging or discharging, the voltage of the lithium battery may fluctuate. Especially when the current is large, standing can allow the voltage to gradually stabilize, avoiding inaccurate test results caused by instantaneous fluctuations; (3) Standing can make the internal chemical state of the battery return to a more natural state, reducing the influence of "memory fatigue"; (4) During the charge and discharge process, the lithium battery may generate heat, resulting in a temperature rise. Standing can allow the battery to cool down and return to room temperature, avoiding the influence of temperature changes on test results; (5) The dynamic charge and discharge process may introduce some dynamic interferences, such as instantaneous current fluctuations or voltage drifts. Standing can eliminate these interferences and ensure the accuracy of subsequent tests. The first preset standing duration can be set according to the characteristics of the internal chemical substances of the lithium battery, the magnitude of the charge and discharge current and voltage, and the charge and discharge duration. For example, the first preset standing duration is set to 10 minutes.

[0080] Fourth, charge the lithium battery that has stood for the first preset standing duration at a first current in a constant current manner;

[0081] Finally, when the lithium battery reaches the preset protection voltage, if the constant current charging stops, a function test result indicating that the basic function of the lithium battery is normal is obtained; otherwise, a function test result indicating that the basic function of the lithium battery is abnormal is obtained.

[0082] In this embodiment, the preset protection voltage refers to a specific voltage value set to protect the lithium battery from damage during the charge and discharge process of the battery. When the lithium battery reaches this voltage, the charge or discharge process will stop. The selection of the cut-off voltage usually depends on the type of lithium battery, application requirements, and specific regulations of the enterprise. According to different standards to be met, the enterprise can stipulate different cut-off voltages. When the lithium battery reaches the preset protection voltage, if the constant current charging stops, it means that the preset protection voltage can play the expected protection role, and the basic function of the lithium battery is normal; otherwise, the basic function of the lithium battery is abnormal.

[0083] In this embodiment, if the functional test result indicates that the basic functions of the lithium battery are normal, subsequent tests can continue. Please continue to refer to Figure 2 , step S102 includes the following sub-steps:

[0084] Sub-step S1020: Continue to charge and discharge the lithium battery with a second current to obtain a DC internal resistance test value of the lithium battery. The second current is greater than the first current;

[0085] In this embodiment, the second current can be a current greater than or equal to 3C. Since the currents of 0.5C, 1C, and 2C have been introduced previously, the current of 3C can be understood based on the above introduction and will not be elaborated here.

[0086] In this embodiment, the second current is greater than the first current. On the one hand, it is to change the current during the test to avoid "memory fatigue". On the other hand, a larger current is used to test the DC internal resistance of the lithium battery, so that the obtained DC internal resistance test value can reflect a more real dynamic internal resistance value, improve the test efficiency, simulate high-power operating conditions, and make the test more comprehensive.

[0087] Sub-step S1021: Continue to charge and discharge the lithium battery with a third current to obtain a capacity test value of the lithium battery. The third current is less than the second current;

[0088] In this embodiment, since a current of 1C represents 1 times the rated capacity of the lithium battery, it can avoid the multiple conversions for currents of other multiples, thereby avoiding the errors caused by the conversions. As an implementation manner, the third current can be a current of 1C.

[0089] Sub-step S1022: Continue to charge and discharge the lithium battery with a fourth current to obtain a voltage drop rate test value of the lithium battery.

[0090] In this embodiment, the fourth current can be a current less than or equal to 1C. The fourth current and the first current can be the same or different.

[0091] As an implementation manner, the first current in the above sub-step S1010 is less than or equal to 1C, the second current in the above sub-steps S1020 - S1022 is greater than or equal to 2C, the third current is 1C, and the fourth current is less than or equal to 1C.

[0092] The reason for conducting the tests in the order of first measuring the DC resistance, then the capacity, and finally the voltage drop rate is as follows: (1) During the test process, the lithium current can change both from low to high and from high to low, increasing the diversity of current changes; (2) Measuring the DC internal resistance first can quickly evaluate the basic health status of the battery, requiring a relatively short time and having no obvious impact on subsequent tests of lithium batteries; then measuring the capacity, the capacity test may cause polarization effects (chemical polarization and concentration polarization) of the battery, thus affecting the DC internal resistance test. Therefore, the capacity test is placed after the DC internal resistance test to avoid the capacity test affecting the DC internal resistance test; finally, measuring the voltage drop rate, the voltage drop rate test takes the longest time, so it is placed last, which can maximize the overall test efficiency. Conducting the tests in the above order can not only reduce the cumulative impact of the tests on the performance of lithium batteries, ensure the accuracy and authenticity of test data, improve the consistency of lithium battery sorting results, but also minimize the test time, improve the test efficiency, and thus improve the sorting efficiency of lithium batteries.

[0093] In this embodiment, the DC internal resistance includes the discharge DC internal resistance and the charge DC internal resistance. To conduct a more detailed test and evaluation of lithium batteries, an implementation method for obtaining the DC internal resistance test value of a lithium battery in this embodiment can be:

[0094] First, discharge the lithium battery at a second current in a constant current manner until the discharge duration reaches a preset cut-off duration to obtain the discharge DC internal resistance of the lithium battery.

[0095] In this embodiment, the preset cut-off duration is used to ensure that the constant current charge and discharge of the lithium battery can reach the charge and discharge completion condition. For constant current discharge, discharge the lithium battery at a second current for a preset cut-off duration. At this time, the power of the lithium battery is basically completely discharged. In a specific scenario, when the lithium battery reaches the discharge completion condition, its voltage will be close to 1.5V.

[0096] The preset cut-off duration can be determined according to the actual parameters of the lithium battery and the second current. Generally speaking, the larger the second current, the shorter the discharge duration required, that is, the shorter the preset cut-off duration. However, although increasing the discharge current can speed up the discharge speed, excessive increase may bring a series of problems, such as increased heating, capacity attenuation, and even safety hazards. Therefore, the second current cannot be increased indefinitely. For example, when the second current is 3C and the preset cut-off duration is set to 10 seconds, it can not only discharge quickly but also pose no safety hazard to the lithium battery.

[0097] In this embodiment, the discharge DC internal resistance refers to a resistance characteristic exhibited during the discharge process of the lithium battery due to the presence of internal materials and structures of the lithium battery.

[0098] Secondly, let the lithium battery after constant current discharge stand for a second preset standing duration;

[0099] In this embodiment, according to the different currents used for discharging, the second preset static duration is also different. The greater the current used for discharging, the longer the second preset static duration needs to be set, and at the same time, the time required for testing will also become longer. Therefore, it is necessary to find a balance between the setting of the second current and the second preset static duration, so that the discharging speed is neither too slow nor causes the second preset static duration to be lengthened, which instead reduces the testing efficiency. As a way of implementation, when the second current is 3C, the second preset static duration can be set to 30 minutes.

[0100] Third, with the second current, perform constant-current charging on the lithium battery after it has been static for the second preset static duration until the charging duration reaches the preset cut-off duration, to obtain the charging DC internal resistance of the lithium battery, and finally obtain the DC internal resistance test value including the discharging DC internal resistance and the charging DC internal resistance.

[0101] In this embodiment, for constant-current charging, with the second current, perform constant-current charging on the lithium battery. After the preset cut-off duration, at this time, the power of the lithium battery is basically fully charged. In a specific scenario, when the lithium battery reaches the condition of being fully charged, its voltage will be close to 2.9V.

[0102] In this embodiment, in order to ensure that the lithium battery is in a stable state before the internal resistance test, to avoid the uneven distribution of chemical substances inside the lithium battery affecting the accuracy of the test results. At the same time, under different SOCs of the lithium battery, its internal chemical environment and electrochemical reaction state will be different. In order to avoid large measurement errors when the lithium battery is at extreme SOCs (extremely low SOC or extremely high SOC), before performing the DC internal resistance test on the lithium battery, this embodiment also provides a processing method to eliminate the problem of inaccurate testing caused by the above factors. The specific implementation method can be:

[0103] Discharge the lithium battery with a preset current so that the voltage of the discharged lithium battery reaches the first preset cut-off voltage, which can be the voltage of the lithium battery when the remaining power of the lithium battery is at the first preset ratio of the total power;

[0104] Let the lithium battery with the voltage reaching the first preset cut-off voltage stand for the first preset static duration.

[0105] In this embodiment, the first preset cut-off voltage can be 50% SOC, and the internal resistance measurement within this range is usually more stable and reliable. Similarly, in order to make the discharged lithium battery return to a stable state, let the discharged lithium battery stand for the first preset static duration. The first preset static duration can be set according to experience. For example, the first preset static duration is set to 10 minutes.

[0106] In an alternative embodiment, the present embodiment further provides a method for obtaining the capacity test value of a lithium battery:

[0107] First, the lithium battery is charged at a third current until the voltage of the lithium battery reaches a first preset stable voltage.

[0108] In the present embodiment, the first preset stable voltage is the voltage value when the lithium battery is fully charged. In a specific scenario, the first preset stable voltage may be 2.8V.

[0109] Second, the lithium battery with the voltage reaching the first preset stable voltage is left standing for a first preset standing duration.

[0110] Finally, the lithium battery after being left standing for the first preset standing duration is discharged at a third current until the voltage of the lithium battery reaches a second preset stable voltage, and the discharge amount of the constant current discharge is obtained and used as the capacity test value.

[0111] In the present embodiment, the second preset stable voltage is the voltage value when the lithium battery is basically discharged. In a specific scenario, the second preset stable voltage may be less than 1.5V and the difference from 1.5V is less than a preset difference.

[0112] In an alternative embodiment, the present embodiment further provides a method for obtaining the voltage drop rate test value of a lithium battery:

[0113] First, the lithium battery is charged at a fourth current until the voltage of the lithium battery reaches a second preset cut-off voltage, where the second preset cut-off voltage is the voltage of the lithium battery when the remaining battery power is a second preset ratio of the total battery power.

[0114] In the present embodiment, the second preset ratio may be 70%, and at this time, the second preset cut-off voltage may be 70% SOC.

[0115] Second, the voltage of the lithium battery is maintained at the second preset cut-off voltage for constant voltage charging until the constant voltage charging duration reaches a preset charging duration or the current of the lithium battery is less than a preset cut-off current, and the first voltage of the lithium battery at this time is obtained.

[0116] In the present embodiment, the end condition of the constant voltage charging is that the constant voltage charging duration reaches the preset charging duration, or the current of the lithium battery is less than the preset cut-off current, and either of these two conditions can end the constant voltage charging. The preset charging duration is the duration for maintaining the voltage of the lithium battery at the second preset cut-off voltage for constant voltage charging so that the lithium battery can finally tend to a stable state. In a scenario, the preset charging duration may be 120 minutes.

[0117] Third, after the lithium battery after constant voltage charging is left standing for a third preset standing duration, obtain the second voltage of the lithium battery at this time;

[0118] In this embodiment, the third preset standing duration can be the minimum duration for the voltage of the fully charged lithium battery to tend to be stable in the self-discharging state. The determination method for the voltage tending to be stable can be that the voltage change within several consecutive preset cycles is not greater than a preset change value. The self-discharging state refers to the phenomenon that the battery capacity of the lithium battery spontaneously decreases due to internal chemical reactions or other physical processes without an external circuit connection.

[0119] Fourth, calculate the measured value of the voltage drop rate according to the first voltage, the second voltage, and the third preset standing duration.

[0120] In this embodiment, as a calculation method, the measured value of the voltage drop rate = (the first voltage - the second voltage) / the third preset standing duration.

[0121] In an alternative embodiment, in order to make the lithium battery in a stable state as much as possible before testing the DC internal resistance, capacity, and voltage drop rate, and thus minimize the influence of the previous stage of testing on the current stage of testing, the lithium battery can be left standing for a preset duration before testing the DC internal resistance, capacity, and voltage drop rate. In a specific scenario, the preset duration can be 10 minutes.

[0122] To fully describe the entire process of the above test, this embodiment is illustrated with a specific example.

[0123] (1) Use the sealed lithium battery with qualified formation data as the battery to be tested, and record the internal resistance and voltage of the battery to be tested. Formation refers to activating the active substances on the surface of the lithium battery electrode through charging and establishing a stable interface layer.

[0124] (2) Prepare a mass production grading equipment for testing.

[0125] (3) Correctly connect the battery core of the lithium battery to be graded to the positive and negative terminal posts of the grading fixture.

[0126] (4) Adjust the temperature of the grading environment to ensure that the grading environment temperature is 25°C ± 2°C.

[0127] (5) The grading process is as follows:

[0128] ① Stand for 5 min and jump to the next step;

[0129] ② Constant current discharge at 1C to the cut-off voltage of 50% SOC, and the time jump condition is 30 min;

[0130] ③ Constant voltage at the 50% SOC value voltage, discharge to the cut-off current of 0.1C, and the time jump condition is 15 min;

[0131] ④ Let it stand for 10 min and then jump to the next working step;

[0132] ⑤ Charge at a constant current of 1C until the cut-off voltage specified by the enterprise; then jump to the next working step;

[0133] ⑥ Let it stand for 10 min and then jump to the next working step;

[0134] ⑦ Discharge at a constant current of 0.5C until the cut-off voltage at 50% SOC, then jump to the next working step;

[0135] ⑧ Let it stand for 10 min and then jump to the next working step;

[0136] ⑨ Discharge at a constant current of 3C for 10 s (discharge completed), then jump to the next working step;

[0137] ⑩ Let it stand for 30 min and then jump to the next working step;

[0138] Charge at a constant current of 3C for 10 s (fully charged), then jump to the next working step;

[0139] Let it stand for 10 min, then jump to the next working step;

[0140] Charge at a constant current of 1C until the voltage reaches 2.8V (conventional and stable), then jump to the next working step;

[0141] Let it stand for 10 min, then jump to the next working step;

[0142] Discharge at a constant current of 1C until the voltage reaches 1.5V, then jump to the next working step;

[0143] Let it stand for 10 min, then jump to the next working step;

[0144] Charge at a constant current of 0.5C until the voltage at 70% SOC value, then jump to the next working step;

[0145] Charge at a constant voltage of 70% SOC value until the cut-off current of 0.1C, and the time jump condition is 120 min;

[0146] Let it stand for 240 min;

[0147] The process ends.

[0148] In the above grading capacitance process, the following four stages are included:

[0149] Stage 1: ① - ⑥ correspond to the basic function tests in the foregoing embodiments. Among them, the 1C in ② and ⑤ is the first current in this embodiment, the cut-off voltage at 50% SOC is the first preset cut-off voltage in this embodiment, 30 min (min stands for minute) is the first discharge duration in this embodiment, the cut-off current of 0.1C is the preset cut-off current in this embodiment, 15 min is the second discharge duration, and the cut-off voltage specified by the enterprise is the preset protection voltage in this embodiment;

[0150] Stage 2: Correspond to the DC internal resistance test in the foregoing embodiments. Among them, the 0.5C in ⑦ is the preset current in this embodiment, the 3C in ⑨ and is the second current in this embodiment, the cut-off time of 10 s is the preset cut-off duration in this embodiment, and the 30 min in ⑩ is the second preset standing duration in this embodiment;

[0151] Stage 3: Correspond to the capacity test in the foregoing embodiments: and the 1C in is the third current in this embodiment, the 2.8V in is the first preset stable voltage in this embodiment, the 1.5V in is the second preset stable voltage in this embodiment;

[0152] Stage 4: Correspond to the voltage drop rate test in the foregoing embodiments: the 0.5C in is the fourth current in this embodiment, and the voltage at 70% SOC value in is the second preset cut-off voltage in this embodiment, the 120 min in is the preset charging duration, the 240 min in is the third preset standing duration.

[0153] In the above Stages 1 to 4, the 10 min in ⑥, is the preset duration; the 10 min in ④, ⑧, is the first preset standing duration.

[0154] (6) After the grading process ends, export the discharge capacity of the th working step as the capacity test value of the lithium battery to be tested, calculate the DCR internal resistances of the charging and discharging processes in ⑨, which are the discharge DC internal resistance and the charging DC internal resistance respectively, take the voltage of the lithium battery to be tested at the end of the as the first voltage, take the voltage of the lithium battery to be tested at the end of as the second voltage, and according to the first voltage, the second voltage and Calculate the test value of the voltage drop rate within 240 minutes in

[0155] (7) Test the AC voltage internal resistance of the lithium battery to be tested, and group and store it according to information such as the capacity test value, DCR internal resistance, and voltage drop rate test value.

[0156] In an alternative embodiment, there are multiple lithium batteries. After obtaining the DC internal resistance test value, capacity test value, and voltage drop rate test value of each lithium battery, this embodiment provides an implementation method for sorting multiple lithium batteries. Please refer to Figure 3 , Figure 3 which is a flowchart example of the lithium battery sorting method provided in this embodiment Figure 3 , and step S103 includes the following sub-steps:

[0157] Sub-step S1030: Group the multiple lithium batteries according to the capacity test value to obtain at least one first group;

[0158] Sub-step S1031: Continue to group the lithium batteries in each first group according to the DC internal resistance test value to obtain at least one second group;

[0159] Sub-step S1032: Continue to group the lithium batteries in each second group according to the voltage drop rate test value to obtain at least one third group;

[0160] Sub-step S1033: Use all the third groups as the sorting result for sorting the multiple lithium batteries.

[0161] It can be understood that after obtaining the DC internal resistance test value, capacity test value, and voltage drop rate test value of multiple lithium batteries, before sorting them, lithium batteries that do not meet the basic conditions can be excluded first, and then the lithium batteries that meet the basic conditions can be sorted. Taking the capacity test value as an example, it is stipulated that lithium batteries with a capacity test value outside the preset capacity range are unqualified lithium batteries, and lithium batteries with a capacity test value outside this preset capacity range need to be excluded and not allowed to participate in the sorting. The same applies to the DC internal resistance test value and the voltage drop rate test value, which will not be elaborated here.

[0162] This embodiment uses an example to illustrate the sorting process. Please refer to Figure 4 , Figure 4 which is an example diagram of the lithium battery sorting process provided in this embodiment, Figure 4Among them, there are a total of 10 lithium batteries, numbered 1 - 10 respectively. First, according to the capacity test values, they are divided into two first groups. The serial numbers of the lithium batteries in each first group are: (1, 2, 3, 4, 5, 6) and (7, 8, 9, 10); for each first group, they are further grouped according to the DC internal resistance test values. (1, 2, 3, 4, 5, 6) is divided into 2 second groups: (1, 4, 6) and (2, 3, 5), and (7, 8, 9, 10) is divided into 2 groups: (7, 8, 9) and (10); for each second group, they are further grouped according to the voltage drop rate test values. (1, 4, 6) is divided into 2 third groups: (1, 4) and (6), (2, 3, 5) is divided into 1 third group: (2, 3, 5), (7, 8, 9) is divided into 2 third groups: (7) and (8, 9), and (10) is divided into 1 third group: (10). The final sorting result is (1, 4), (6), (2, 3, 5), (7), (8, 9), (10).

[0163] In summary, the embodiment of the present invention provides a method for sorting lithium batteries. The method includes: performing basic function tests on lithium batteries; if the basic functions of the lithium batteries are normal, then sequentially performing DC internal resistance tests, capacity tests, and voltage drop rate tests on the lithium batteries to obtain the DC internal resistance test values, capacity test values, and voltage drop rate test values of the lithium batteries; sorting the lithium batteries according to the DC internal resistance test values, capacity test values, and voltage drop rate test values. Compared with the prior art, this embodiment has at least the following advantages: (1) By sequentially obtaining the DC internal resistance test values, capacity test values, and voltage drop rate test values of lithium batteries during continuous tests to sort the lithium batteries, since the target lithium batteries are sorted and evaluated from various index dimensions such as the functions, DC internal resistance, capacity, and voltage drop rate of the target lithium batteries, the final sorting consistency can be ensured; (2) During continuous tests, on the premise of meeting the test requirements, by changing the current, this kind of "memory fatigue" caused by the fixed current is avoided, improving the accuracy and effectiveness of the test results, and facilitating the discovery of the defective states of lithium batteries, improving the comprehensiveness of the test; (3) Different resting times are set for lithium batteries in different situations, which not only ensures that the test time will not be too long, but also ensures that the lithium batteries are in a stable state before each test, so as to prevent the previous test from affecting the next test; (4) The tests are carried out in the order of first measuring the DC resistance, then measuring the capacity, and finally measuring the voltage drop rate, which not only reduces the cumulative impact of the tests on the performance of lithium batteries, ensures the accuracy and authenticity of the test data, improves the consistency of the sorting results of lithium batteries, but also minimizes the test time, improves the test efficiency, and further improves the sorting efficiency of lithium batteries.

[0164] As described above, these are only various embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should all be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A lithium battery sorting method, characterized in that: The method comprises: Conduct basic functional tests on lithium batteries; If the basic functions of the lithium battery are normal, the lithium battery is sequentially subjected to a DC internal resistance test, a capacity test, and a voltage drop rate test to obtain a DC internal resistance test value, a capacity test value, and a voltage drop rate test value of the lithium battery; The lithium batteries are sorted according to the DC internal resistance test value, the capacity test value and the voltage drop rate test value.

2. The lithium battery sorting method according to claim 1, characterized in that: The steps of performing basic functional testing on the lithium battery include: Charging and discharging the lithium battery with a first current to obtain a function test result; If the basic functions of the lithium battery are normal, the steps of sequentially performing a DC internal resistance test, a capacity test, and a voltage drop rate test on the lithium battery to obtain a DC internal resistance test value, a capacity test value, and a voltage drop rate test value of the lithium battery include: If the functional test result indicates that the basic function of the lithium battery is normal, the lithium battery is continuously charged and discharged with a second current to obtain a DC internal resistance test value of the lithium battery, and the second current is greater than the first current; Continue charging and discharging the lithium battery with a third current to obtain a capacity test value of the lithium battery, wherein the third current is less than the second current; The lithium battery is continuously charged and discharged with a fourth current to obtain a voltage drop rate test value of the lithium battery.

3. The lithium battery sorting method according to claim 2, characterized in that: The step of charging and discharging the lithium battery with a first current to obtain a function test result comprises: The lithium battery is discharged at a constant current with the first current until the constant current discharge duration reaches a first discharge duration or the voltage of the lithium battery reaches a first preset cut-off voltage, wherein the first preset cut-off voltage is the voltage of the lithium battery when the remaining power of the lithium battery is a first preset proportion of the total power; Maintaining the voltage of the lithium battery at the first preset cut-off voltage, and performing constant voltage discharge until the constant voltage discharge duration reaches a second discharge duration or the current of the lithium battery is less than the preset cut-off current; Allowing the lithium battery after constant voltage discharge to stand for a first preset standing time; Using the first current, constant-current charging is performed on the lithium battery after the first preset resting time; When the lithium battery reaches the preset protection voltage, if the constant current charging is stopped, the functional test result indicating that the basic function of the lithium battery is normal is obtained, otherwise the functional test result indicating that the basic function of the lithium battery is abnormal is obtained.

4. The lithium battery sorting method according to claim 2, characterized in that: If the functional test result indicates that the basic function of the lithium battery is normal, the step of continuing to charge and discharge the lithium battery with a second current to obtain a DC internal resistance test value of the lithium battery includes: Discharging the lithium battery at a constant current with the second current until the discharge duration reaches a preset cut-off duration, thereby obtaining a discharge DC internal resistance of the lithium battery; Allowing the lithium battery after constant current discharge to stand for a second preset standing time; The lithium battery after being left standing for the second preset standing time is charged with constant current using the second current until the charging time reaches the preset cut-off time, thereby obtaining the charging DC internal resistance of the lithium battery, and finally obtaining the DC internal resistance test value including the discharge DC internal resistance and the charging DC internal resistance.

5. The lithium battery sorting method according to claim 4, characterized in that: Before the step of performing constant current discharge of the lithium battery with the second current until the discharge duration reaches a preset cut-off duration and obtaining the discharge DC internal resistance of the lithium battery, the method includes: Discharging the lithium battery with a preset current so that the voltage of the lithium battery after discharge reaches a first preset cut-off voltage, wherein the first preset cut-off voltage is the voltage of the lithium battery when the remaining power of the lithium battery is a first preset proportion of the total power; The lithium battery whose voltage reaches the first preset cut-off voltage is left to stand for a first preset standing time.

6. The lithium battery sorting method according to claim 2, characterized in that: The step of continuously charging and discharging the lithium battery with the third current to obtain a capacity test value of the lithium battery comprises: Using the third current, the lithium battery is charged at a constant current until the voltage of the lithium battery reaches a first preset stable voltage; Allowing the lithium battery whose voltage reaches the first preset stable voltage to stand for a first preset standing time; The lithium battery after being stationary for the first preset stationary time is discharged at a constant current with the third current until the voltage of the lithium battery reaches a second preset stable voltage, and a discharge amount of the constant current discharge is obtained and used as the capacity test value.

7. The lithium battery sorting method according to claim 2, characterized in that: The step of continuing to charge and discharge the lithium battery with the fourth current to obtain a voltage drop rate test value of the lithium battery comprises: The lithium battery is charged at a constant current with the fourth current until the voltage of the lithium battery reaches a second preset cut-off voltage, where the second preset cut-off voltage is the voltage of the lithium battery when the remaining power of the lithium battery is a second preset proportion of the total power; Maintaining the voltage of the lithium battery at the second preset cut-off voltage, performing constant voltage charging until the constant voltage charging time reaches the preset charging time or the current of the lithium battery is less than the preset cut-off current and obtaining the first voltage of the lithium battery at this time; After the constant voltage charged lithium battery is left to stand for a third preset standing time, a second voltage of the lithium battery is obtained; The voltage drop rate test value is calculated according to the first voltage, the second voltage and the third preset static time.

8. The lithium battery sorting method according to any one of claims 2 to 7, characterized in that: Before the step of continuing to charge and discharge the lithium battery, the method includes: The lithium battery is left to stand for a preset period of time.

9. The lithium battery sorting method according to any one of claims 2 to 7, characterized in that: The first current is less than or equal to 1C, the second current is greater than or equal to 2C, the third current is 1C, and the fourth current is less than or equal to 1C.

10. The lithium battery sorting method according to claim 1, characterized in that: There are a plurality of lithium batteries, and the step of sorting the lithium batteries according to the DC internal resistance test value, the capacity test value, and the voltage drop rate test value comprises: According to the capacity test values, the plurality of lithium batteries are grouped to obtain at least one first group; According to the DC internal resistance test value, further grouping the lithium batteries in each of the first groups to obtain at least one second group; According to the voltage drop rate test value, further grouping the lithium batteries in each of the second groups to obtain at least one third group; All the third groups are used as the sorting results of sorting the plurality of lithium batteries.

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