A rapid non-destructive detection method for lithium ion battery lithium precipitation

Abstract

The application discloses a kind of quick nondestructive testing methods of lithium ion battery lithium precipitation, comprising the following steps: step S1, for target battery, preset number of charge-discharge cycle test is carried out, battery voltage V in the process of testing is collected in real time in discharge process, and discharge time t is recorded;Step S2, after each charge-discharge cycle test, respectively with voltage V to discharge time t is differentiated, obtains dV / t, with dV / t as ordinate, with t as abscissa, draw the discharge voltage change rate curve of target battery in each charge-discharge cycle test;Step S3, for the discharge voltage change rate curve of charge-discharge cycle test, whether lithium ion battery occurs lithium precipitation is judged by judging whether the rise ratio of characteristic point peak value is greater than preset rise ratio threshold value.The application can solve the problem that existing detection lithium precipitation method is time-consuming and laborious, and the accuracy is low, whether lithium ion battery occurs lithium precipitation can be quickly and accurately judged.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a rapid non-destructive detection method for lithium deposition in lithium ion batteries. Background Art

[0002] At present, lithium-ion batteries have been widely used in digital products, electric vehicles and energy storage fields due to their advantages such as high energy density, good cycle performance and green and pollution-free.

[0003] With the continuous advancement of lithium-ion power battery technology and increasingly fierce market competition, higher requirements are placed on current new energy batteries. The main trend is to significantly improve energy density, long cycle, fast charging and safety performance.

[0004] However, during high-rate charging, low-temperature charging, and long cycles, lithium-ion power batteries can experience lithium deposition on the negative electrode surface as polarization gradually increases. This deposition of lithium dendrites can increase internal resistance, rapidly decay capacity, and even pierce the diaphragm, leading to internal short circuits and thermal runaway safety hazards. Therefore, it is extremely important to quickly identify and assess lithium deposition on the negative electrode graphite surface during battery system design and product development.

[0005] Existing technologies for detecting lithium deposition in batteries mainly include disassembly and non-destructive testing. Among them, the disassembly method usually involves dissecting the battery and observing the surface state of the negative electrode graphite to determine whether lithium deposition has occurred. This method is time-consuming and labor-intensive, and requires additional physical and chemical analysis and characterization to confirm lithium deposition. In addition, existing non-destructive testing technologies mainly use capacity retention, coulombic efficiency, and battery aging data for indirect calculations, and use methods such as the voltage difference before and after standing or the constant current charging ratio to determine whether lithium deposition has occurred. However, this method is complex and has low accuracy. Summary of the Invention

[0006] The purpose of the present invention is to provide a rapid non-destructive detection method for lithium deposition in lithium ion batteries in response to the technical defects of the prior art.

[0007] To this end, the present invention provides a rapid non-destructive detection method for lithium deposition in lithium ion batteries, comprising the following steps:

[0008] Step S1, performing a preset number of charge-discharge cycle tests on the target battery to be tested. During each charge-discharge cycle test, the voltage V of the target battery during the discharge process is collected in real time, and the discharge time t corresponding to each voltage V is recorded simultaneously;

[0009] Step S2: After each charge-discharge cycle test, the discharge time t is differentiated by the voltage V of the target battery during the discharge process of the charge-discharge cycle test to obtain dV / t. Then, a discharge voltage change rate curve of the target battery in each charge-discharge cycle test is plotted with dV / t as the ordinate and the discharge time t as the abscissa, thereby obtaining the discharge voltage change rate curve for all charge-discharge cycle tests.

[0010] Step S3, for the discharge voltage change rate curves of the charge and discharge cycle tests of all the cycles obtained in step S2, determine whether there is a discharge voltage change rate curve in which the increase ratio of the characteristic point peak is greater than a preset increase ratio threshold; if so, it is determined that lithium plating has occurred in the lithium-ion battery; if not, it is determined that lithium plating has not occurred in the lithium-ion battery.

[0011] Preferably, in step S1, each charge-discharge cycle test includes a constant current and constant voltage charging operation, a first static operation of a preset time, a constant current discharge operation, and a second static operation of a preset time.

[0012] The constant current and constant voltage charging operation is specifically as follows: charging the target battery with constant current and constant voltage to 100% SOC;

[0013] The constant current discharge operation is specifically: constant current discharge to empty charge 0% SOC.

[0014] Preferably, in step S1, the constant current and constant voltage charging operation, the first static operation of a preset time, the constant current discharging operation and the second static operation of a preset time are all performed under a constant temperature condition;

[0015] The constant temperature is 23-27℃, and the temperature error is ±2℃.

[0016] Preferably, in step S3, for the discharge voltage change rate curve of the target battery in any charge and discharge cycle test, the calculation formula for the increase ratio A of the peak value of the characteristic point is as follows:

[0017] A=(BC) / C;

[0018] Wherein, B is the peak value of the crest point in the discharge voltage rate of change curve of the charge-discharge cycle test, and the crest point is the point with the minimum dV / dt value in the discharge voltage rate of change curve of the charge-discharge cycle test;

[0019] C is the peak value of the initial peak point in the discharge voltage change rate curve of the target battery in the first charge and discharge cycle test. The initial peak point is the point with the smallest dV / dt value in the discharge voltage change rate curve of the first charge and discharge cycle test.

[0020] Preferably, in step S3, the preset increase ratio threshold is 74%.

[0021] It can be seen from the technical solution provided by the present invention that, compared with the prior art, the present invention provides a rapid and non-destructive detection method for lithium deposition in lithium-ion batteries. The method is scientifically designed and can solve the problems of the existing lithium deposition detection methods being time-consuming, labor-intensive, and having low accuracy. It can quickly and accurately determine whether lithium deposition has occurred in lithium-ion batteries, and has great practical significance. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A flowchart of a method for rapid nondestructive detection of lithium deposition in lithium-ion batteries provided by the present invention;

[0023] Figure 2 A rapid nondestructive detection method for lithium plating in a lithium-ion battery provided by the present invention is provided, and a schematic diagram of the discharge time differential voltage curve (i.e., the discharge voltage rate of change curve) of the target battery in Example 1;

[0024] Figure 3 A rapid nondestructive detection method for lithium plating in a lithium-ion battery provided by the present invention is provided, and a schematic diagram of the discharge time differential voltage curve (i.e., the discharge voltage rate of change curve) of the target battery in Example 2;

[0025] Figure 4 Schematic diagram of the discharge time differential voltage curve (i.e., discharge voltage change rate curve) of a normal battery without lithium deposition. DETAILED DESCRIPTION

[0026] In order to enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and implementation methods.

[0027] See also Figures 1 to 4 The present invention provides a rapid non-destructive detection method for lithium deposition in lithium-ion batteries, comprising the following steps:

[0028] Step S1, performing a preset number of charge-discharge cycle tests on the target battery to be tested. During each charge-discharge cycle test, the voltage V of the target battery during the discharge process is collected in real time, and the discharge time t corresponding to each voltage V is recorded simultaneously (i.e., the discharge time corresponding to the voltage V after the discharge operation of each charge-discharge cycle test begins);

[0029] Step S2: After each charge-discharge cycle test, the discharge time t is differentiated by the voltage V of the target battery during the discharge process of the charge-discharge cycle test to obtain dV / t. Then, a discharge voltage change rate curve of the target battery in each charge-discharge cycle test is plotted with dV / t as the ordinate and the discharge time t as the abscissa, thereby obtaining the discharge voltage change rate curve for all charge-discharge cycle tests.

[0030] Step S3, for the discharge voltage change rate curves of the charge and discharge cycle tests of all the cycles obtained in step S2, determine whether there is a discharge voltage change rate curve in which the increase ratio of the characteristic point peak is greater than a preset increase ratio threshold; if so, it is determined that lithium plating has occurred in the lithium-ion battery; if not, it is determined that lithium plating has not occurred in the lithium-ion battery.

[0031] In step S1, a charge-discharge cycle test is performed on a target battery using existing charge-discharge equipment. The existing charge-discharge equipment can record the battery voltage and the corresponding charge-discharge time in real time during the charge-discharge process of the battery.

[0032] In step S1, in specific implementation, each charge and discharge cycle test includes a constant current and constant voltage charging operation, a first static operation of a preset time, a constant current discharge operation, and a second static operation of a preset time.

[0033] The constant current and constant voltage charging operation is specifically as follows: charging the target battery with constant current and constant voltage to 100% SOC;

[0034] The constant current discharge operation is specifically: constant current discharge to empty charge 0% SOC.

[0035] It should be noted that the repetitive, preset number of charge and discharge cycle tests are continuous charge and discharge processes. Each charge and discharge cycle test consists of: first fully charging, then resting, then discharging, and then resting again.

[0036] In step S1, in a specific implementation, the rest time of the battery is controlled, and the battery voltage collection interval is not limited.

[0037] In step S1, in specific implementation, the constant current and constant voltage charging operation, the first static operation of the preset time, the constant current discharging operation and the second static operation of the preset time are all under constant temperature conditions;

[0038] The constant temperature is 23-27℃, and the temperature error is ±2℃.

[0039] In step S3, in a specific implementation, for the discharge voltage change rate curve of the target battery in any charge and discharge cycle test, the calculation formula for the increase ratio A of the peak value of the characteristic point is as follows:

[0040] A=(BC) / C;

[0041] Wherein, B is the peak value of the crest point in the discharge voltage rate of change curve of the charge-discharge cycle test. The crest point is the point (position point) with the minimum dV / dt value in the discharge voltage rate of change curve of the charge-discharge cycle test. The peak value of the crest point is the peak value dV / dt of the point with the minimum dV / dt value in the discharge voltage rate of change curve of the charge-discharge cycle test.

[0042] C is the peak value of the initial peak point in the discharge voltage rate of change curve of the target battery in the first charge and discharge cycle test. The initial peak point is the point (position point) with the smallest dV / dt value in the discharge voltage rate of change curve of the first charge and discharge cycle test. The peak value of the initial peak point is the peak value dV / dt of the point with the smallest dV / dt value in the discharge voltage rate of change curve of the first charge and discharge cycle test.

[0043] It should be noted that the peak point in a discharge voltage change rate curve is the point in the curve where the dV / dt value is the smallest.

[0044] In step S3, in specific implementation, a threshold of the increase ratio is preset, preferably 74%.

[0045] It should be noted that, for the present invention, by analyzing the cycle test data of a large number of batteries and processing the data, the dV / dt~t curve is drawn to obtain the discharge dV / dt curve in the embodiment, and the data and curve are summarized. After summarizing the rules, a large amount of calculated data results show that the increase ratio A>74% of the peak value of the characteristic point is the critical point. In addition, combined with practice, it can be concluded that after the continuous disassembly of the above large number of batteries, lithium plating was found in the negative electrode of the battery, which once again verified the reliability and stability of the theoretical value. Therefore, the preset increase ratio threshold (ie, critical value) is selected as 74%.

[0046] It should be noted that the purpose of conducting non-destructive testing in the method of the present invention is that, on the one hand, if lithium deposition in the battery is not discovered in time, it may cause continuous large-scale lithium deposition, increased internal resistance, accelerated heat generation, and lithium deposition is considered to be the main factor in battery performance degradation, thereby reducing the battery cycle life and even causing battery safety accidents; on the other hand, using a non-destructive battery method to detect lithium deposition is a simpler and more effective solution, which can detect the loss of active lithium in the lithium-ion battery before the capacity of the lithium-ion battery drops rapidly, thereby experimentally predicting the capacity drop of the lithium-ion battery at an early stage, and then reducing lithium deposition and battery degradation through mitigation response plans.

[0047] In step S3, specifically, for the discharge voltage change rate curves of all the charge and discharge cycle tests obtained in step S2, if the increase ratio of the peak value of the characteristic point in the multi-cycle discharge voltage change rate curve (i.e., multiple discharge voltage change rate curves) is greater than the preset increase ratio threshold, it is judged that during the charge and discharge cycle test process with the highest number of cycles, lithium plating of the lithium-ion battery begins to occur.

[0048] It should be noted that the peak error of the discharge time differential voltage curve (i.e., the discharge voltage change rate curve) of the target battery is within 5%. If the increase ratio A of the peak values ​​of the characteristic points of several discharge voltage change rate curves is within the fluctuation range (i.e., the range of 69%-74%), the target battery may only undergo lithium deposition. If it exceeds the fluctuation range, the target battery will definitely undergo lithium deposition.

[0049] It should be noted that the peak error of the discharge time differential voltage curve (i.e., the discharge voltage rate of change curve) of the target battery is 5%. The reasons are: first, it is believed that it is caused by test errors during the test process, such as poor battery connection problems and increased internal resistance; second, it is caused by factors such as self-discharge and poor appearance caused by problems with the battery itself. The purpose is to eliminate the influence of these factors, resulting in inaccurate data. When the increase ratio A of the peak value of the characteristic point of the discharge voltage rate of change curve is in the range of 69%-74% (i.e., within the peak error of 5%), lithium plating may exist due to test data errors, and the probability of occurrence is very small; when the increase ratio A>74%, it is judged that the target battery must have lithium plating.

[0050] It should be noted that, for the present invention, during the continuous cyclic charge and discharge process of the target battery, the degree of lithium precipitation becomes more obvious as the number of cycles increases. Therefore, in order to non-destructively determine the lithium precipitation state, the number of cycles needs to be continuously increased to simulate the continuous use process of the target battery.

[0051] Based on the above technical solutions, it can be seen that the technical solution provided by the present invention can quickly, non-destructively and simply detect the risk of lithium plating, improve detection efficiency, and do not require the battery to be disassembled, thereby improving safety. In addition, during the cycle process, the battery usage process is simulated, and the increase ratio of the characteristic point peak in the time differential voltage curve (i.e., the discharge voltage rate of change curve) is monitored to see whether it is greater than the preset increase ratio threshold to confirm whether the battery has lithium plating during the charge and discharge process, and to evaluate the battery's health status in a more reasonable and accurate manner.

[0052] In order to more clearly understand the technical solution of the present invention, the technical solution of the present invention is described below through specific embodiments.

[0053] Example 1.

[0054] The present invention provides a rapid non-destructive detection method for lithium deposition in lithium-ion batteries, which uses a 40Ah square battery (aluminum shell lithium iron phosphate battery cell) as the target battery for detection, and specifically includes the following steps:

[0055] First, the square battery was subjected to a charge and discharge cycle test at room temperature, using constant current and constant voltage charging-resting-constant current discharge-resting, and this process was repeated.

[0056] Then, the target battery to be tested is first charged with a preset charging current at constant current and constant voltage to 3.65V, with a current cutoff of 0.05C, that is, 100% SOC, and allowed to stand for 0.5h. Then, it is discharged with a preset constant current to 2.0V, 0% SOC, and allowed to stand for 0.5h. During the repeated complete charging and discharging process, the voltage V and time t data during the charging and discharging period per second, that is, V~t, are recorded, and the V~t data are subjected to second-order differential processing to obtain a dV / dt~t curve, that is, using dV / dt as the vertical coordinate and the battery discharge time t as the horizontal coordinate, and a time differential voltage dV / dt curve (that is, a discharge voltage change rate curve) of the interval number of cycles is plotted in a graph, specifically including the curves of the 1st to 120th cycles.

[0057] See also Figure 2 Among the multiple discharge time differential voltage curves dV / dt (i.e., discharge voltage change rate curves) shown, the peak value dV / dt of the discharge time differential voltage curve corresponding to the 25th (i.e., 25th cycle) charge and discharge cycle (i.e., the peak value dV / dt of the 25th curve) has a peak value increase ratio of >74% for the first time, and it is detected that the target battery has begun to undergo lithium plating. When the number of cycles is relatively small, the lithium plating battery belongs to the slow lithium plating period, and the discharge rate is accelerated, indicating that the discharge speed is reduced, and the discharge process is gradually accelerated. Before 50 cycles, the dV / dt curve trend is normal, and the subsequent cycle curve begins to jump, and the curve has signals such as inflection points, and the voltage response rate is accelerated, indicating that lithium plating is intensified during the cycle. Due to the occurrence of lithium plating, the active lithium source is lost, resulting in the inability of lithium ions to be completely embedded in the graphite negative electrode, resulting in an accelerated discharge rate and a rapid voltage response time.

[0058] See also Figure 4 The discharge time differential voltage curve dV / dt curve of a normal non-deposition lithium battery during normal discharge is shown in the figure. The battery peak is basically stable, with no abnormal points, no curve step phenomenon, and the peak increase ratio is <74%.

[0059] In this embodiment 1, the normal non-lithium-evolving battery and the target battery to be tested are batteries belonging to the same battery system; it should be noted that, for the present invention, a battery of the same battery system as the target battery to be tested (such as a lithium iron phosphate system with the same chemical system or a developed battery of the same model) is taken as a normal non-lithium-evolving battery (i.e., a reference battery in product development, which is used as an evaluation benchmark).

[0060] In this embodiment 1, batteries of the same battery system refer to cells of the same specifications and models, that is, cells with the same dimensions and chemical system. For example, all of them are lithium iron phosphate system batteries (prismatic aluminum shell lithium iron phosphate cells) with the LP27148134 size. Other batteries of the same size (soft pack, cylindrical) and with the same chemical system can also be used as needed.

[0061] Example 2.

[0062] The present invention provides a rapid non-destructive detection method for lithium deposition in lithium-ion batteries, which uses a 40Ah square battery (aluminum shell lithium iron phosphate battery cell) as the target battery for detection, and specifically includes the following steps:

[0063] First, the square battery was subjected to a charge and discharge cycle test at room temperature, using constant current and constant voltage charging-resting-constant current discharge-resting, and this process was repeated.

[0064] Then, the target battery was charged with constant current and constant voltage to 3.65V, 0.05C current cutoff, 100% SOC, and rested for 0.5h, and then discharged with constant current to 2.0V, 0% SOC, and rested for 0.5h. During the repeated complete charge and discharge process, the voltage and time data, i.e., Vt, were recorded every second during the charge and discharge period. The Vt data was subjected to second-order differential processing to obtain the dV / dt~t curve (i.e., the discharge voltage change rate curve), specifically including the curves from the 1st to the 120th cycle.

[0065] See also Figure 3Among the multiple discharge time differential voltage curves dV / dt (i.e., discharge voltage change rate curves) shown, the peak value dV / dt of the discharge time differential voltage curve corresponding to the 20th (i.e., 20th cycle) charge and discharge cycle (i.e., the peak value dV / dt of the 20th curve) has a peak value increase ratio of >74% for the first time, and it is detected that the target battery has begun to undergo lithium plating. When the number of cycles is relatively small, the lithium plating battery belongs to the slow lithium plating period, and the discharge rate is accelerated, indicating that the discharge speed is reduced, and the discharge process is gradually accelerated. Before 60 cycles, the dV / dt curve trend is normal, and the subsequent cycle curve begins to jump, and the curve has signals such as inflection points, and the voltage response rate is accelerated, indicating that lithium plating is intensified during the cycle. Due to the occurrence of lithium plating, the active lithium source is lost, resulting in the inability of lithium ions to be completely embedded in the graphite negative electrode, resulting in an accelerated discharge rate and a rapid voltage response time.

[0066] See also Figure 4 The discharge time differential voltage curve dV / dt curve of a normal non-deposition lithium battery during normal discharge is shown in the figure. The battery peak is basically stable, with no abnormal points, no curve step phenomenon, and the peak increase ratio is <74%.

[0067] In this embodiment 2, the normal non-lithium-evolving battery and the target battery to be tested are batteries belonging to the same battery system; it should be noted that, for the present invention, a battery of the same battery system as the target battery to be tested (such as a lithium iron phosphate system with the same chemical system or a developed battery of the same model) is taken as a normal non-lithium-evolving battery (i.e., a reference battery in product development, which is used as an evaluation benchmark).

[0068] In this embodiment 2, batteries of the same battery system refer to cells of the same specifications and models, that is, cells with the same dimensions and chemical system. For example, all of them are lithium iron phosphate system batteries (prismatic aluminum case lithium iron phosphate cells) with the LP27148134 size. Other batteries of the same size (soft pack, cylindrical) and with the same chemical system can also be used as needed.

[0069] In summary, compared with the existing technology, the rapid non-destructive detection method for lithium deposition in lithium-ion batteries provided by the present invention is scientifically designed and can solve the problems of time-consuming, labor-intensive and low-accuracy of existing lithium deposition detection methods. It can quickly and accurately determine whether lithium deposition has occurred in lithium-ion batteries, and has great practical significance.

[0070] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A rapid non-destructive detection method for lithium deposition in lithium-ion batteries, characterized in that: The following steps are involved: Step S1, performing a preset number of charge-discharge cycle tests on the target battery to be tested. During each charge-discharge cycle test, the voltage V of the target battery during the discharge process is collected in real time, and the discharge time t corresponding to each voltage V is recorded simultaneously; Step S2: After each charge-discharge cycle test, the discharge time t is differentiated by the voltage V of the target battery during the discharge process of the charge-discharge cycle test to obtain dV / t. Then, a discharge voltage change rate curve of the target battery in each charge-discharge cycle test is plotted with dV / t as the ordinate and the discharge time t as the abscissa, thereby obtaining the discharge voltage change rate curve for all charge-discharge cycle tests. Step S3, for all the charge and discharge cycle tests obtained in step S2, determine whether there is a discharge voltage change rate curve in which the increase ratio of the characteristic point peak is greater than a preset increase ratio threshold; if so, it is determined that lithium plating has occurred in the lithium-ion battery; if not, it is determined that lithium plating has not occurred in the lithium-ion battery; In step S3, for the discharge voltage change rate curve of the target battery in any charge and discharge cycle test, the calculation formula for the increase ratio A of the peak value of the characteristic point is as follows: A=(BC) / C; Wherein, B is the peak value of the crest point in the discharge voltage rate of change curve of the charge-discharge cycle test, and the crest point is the point with the minimum dV / dt value in the discharge voltage rate of change curve of the charge-discharge cycle test; C is the peak value of the initial peak point in the discharge voltage change rate curve of the target battery in the first charge-discharge cycle test. The initial peak point is the point with the minimum dV / dt value in the discharge voltage change rate curve of the first charge-discharge cycle test; In step S3, the preset increase ratio threshold is 74%.

2. The rapid nondestructive detection method for lithium deposition in a lithium-ion battery according to claim 1, wherein: In step S1, each charge-discharge cycle test includes a constant current and constant voltage charging operation, a first static operation of a preset time, a constant current discharge operation, and a second static operation of a preset time. The constant current and constant voltage charging operation is specifically as follows: charging the target battery with constant current and constant voltage to 100% SOC; Constant current discharge operation, specifically: constant current discharge to empty power 0% SOC.

3. The rapid nondestructive detection method for lithium deposition in a lithium-ion battery as claimed in claim 2, wherein: In step S1, the constant current and constant voltage charging operation, the first static operation of a preset time, the constant current discharging operation and the second static operation of a preset time are all under a constant temperature condition; The constant temperature is 23-27℃, and the temperature error is ±2℃.

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