A non-destructive testing method for lithium plating in lithium-ion batteries and its application.

Abstract

This invention discloses a non-destructive testing method for lithium-ion batteries, comprising the following steps: a charging process of the battery under test, an electrochemical excitation process, and an analysis process. This invention determines whether lithium plating occurs inside the battery based on the change in AC impedance over time during the electrochemical excitation process. When the AC impedance exhibits a step change over time, it indicates that lithium plating has occurred in the lithium-ion battery under test during charging. The detection method in this invention is non-destructive, enabling rapid acquisition of experimental parameters and accurate reflection of lithium plating within the battery. This detection method is applicable to determining charging conditions for lithium-ion batteries without lithium plating, identifying charging parameters such as the maximum charging current and maximum charging voltage during charging, and determining the range of external conditions such as temperature during charging. By using the determined charging parameters, rapid charging of the battery can be achieved without affecting battery performance.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery testing, specifically relating to a non-destructive testing method for lithium plating in lithium-ion batteries and its application method. Background Technology

[0002] New energy technology is a high-tech field of our time. As an important part of the new energy field, the lithium-ion battery industry has attracted attention from all sectors and is also in a period of rapid development. With the widespread application of lithium-ion batteries in various industries and the continuous increase in the market, higher requirements have been put forward for its cost, energy density, rate performance, high and low temperature performance, cycle performance and safety performance.

[0003] Currently, the industry primarily improves the energy density of individual battery cells by using high-nickel cathode materials combined with graphite-silicon hybrid anode materials. This aims to increase energy density while maintaining product reliability. However, with technological advancements and evolving work and lifestyle needs, in addition to energy density requirements, the time cost incurred during battery cell application has become a key performance indicator. Fast charging has become a key expectation for lithium-ion battery performance; simultaneously, wider temperature ranges and longer cycle life are also required. However, lithium-ion batteries are prone to lithium plating under conditions such as high-rate charging, low-temperature charging, or increased polarization after cycling. Lithium plating accelerates battery capacity decay, increases internal resistance, and lithium dendrites may puncture the separator, causing internal short circuits and safety issues. All of these factors accelerate lithium-ion battery aging, leading to reduced performance, battery failure, and potentially even more serious consequences.

[0004] Therefore, analyzing the lithium plating situation inside lithium-ion batteries and setting charging conditions to prevent lithium plating is of great significance to the charging and performance of lithium-ion batteries. Currently, methods for detecting lithium plating in batteries include disassembly and non-destructive testing. Disassembly is a destructive testing method that involves disassembling the battery to determine if lithium plating has occurred inside. This method prevents subsequent analysis and testing after disassembly. More importantly, the disassembly process poses serious safety hazards, easily leading to accidents due to improper operation or poor production environments, resulting in property damage and even endangering the personal safety of workers.

[0005] Currently, disassembly methods are gradually being replaced by non-destructive testing (NDT), which can detect lithium plating in batteries without irreversible disassembly. For example, Chinese invention patent application number 201711141760.4, entitled "Detection Method for Lithium Plating in Lithium-ion Batteries," discloses a method for detecting lithium plating in lithium-ion batteries: the lithium-ion battery to be tested is pre-formed and then placed and sealed, specifically through a first placement; high-current constant-current charging; a second placement; and low-current constant-voltage charging. If a continuous voltage drop occurs at a certain stage during the low-current constant-voltage charging process, the lithium-ion battery to be tested is determined to have lithium plating. While the principle of this method is relatively simple, the placement and sealing time is long, the detection process takes a considerable amount of time, and the detection efficiency is low. For example, Chinese invention patent application number 201210312700.5 entitled "A method for detecting lithium plating in lithium-ion power batteries", and application number 201710342850.3 entitled "A method for detecting lithium plating in batteries, a battery management system and a battery system", discloses a detection method that, without disassembling the lithium-ion battery, obtains appropriate electrical parameters, analyzes the electrical parameters, and then obtains the lithium plating status of the lithium-ion battery.

[0006] The above-mentioned detection methods can all reflect the lithium plating inside lithium-ion batteries under non-destructive conditions. In the testing process of lithium-ion batteries, finding a simple and accurate lithium plating detection method is of great significance for determining the charging conditions of lithium-ion batteries. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a non-destructive testing method for lithium plating in lithium-ion batteries, comprising the following steps: a charging process of the battery under test, an electrochemical excitation process, and an analysis process. This invention determines whether lithium plating occurs inside the battery based on the change in AC impedance over time during electrochemical excitation. A step change in AC impedance over time indicates that lithium plating has occurred in the lithium-ion battery under test during charging. The detection method in this invention is non-destructive, enabling rapid acquisition of experimental parameters and accurate reflection of lithium plating within the battery. This detection method is applicable to determining charging conditions for lithium-ion batteries without lithium plating, identifying charging parameters such as the maximum charging current and maximum charging voltage during charging, and determining the range of external conditions such as temperature during charging. By using the determined charging parameters, rapid charging of the battery can be achieved without affecting battery performance.

[0008] The technical effects to be achieved by this invention are accomplished through the following solutions:

[0009] This invention provides a non-destructive testing method for lithium-ion batteries, comprising the following steps:

[0010] S01, Charging process: Charge the lithium-ion battery under test to the set state;

[0011] S02, Electrochemical excitation process: After charging is completed, an AC electrochemical perturbation signal is intermittently applied to the lithium-ion battery under test and its AC impedance is monitored;

[0012] S03, Analysis process: Analyze the relationship between the AC impedance and time. If the AC impedance shows a step change with time, it indicates that lithium plating occurs in the lithium-ion battery under test during the charging process.

[0013] The use of a lithium-ion battery can be simplified to a continuous cycle of charging, resting, and discharging. During charging, lithium ions are released from the positive electrode, pass through the separator, and gain electrons on the surface of the negative electrode; the discharging process is the opposite, with lithium ions being released from the negative electrode and returning to the positive electrode. Therefore, the deposition of metallic lithium occurs during the battery charging process. This invention focuses on the battery charging process and provides a non-destructive testing method for whether lithium deposition occurs in a lithium-ion battery during charging.

[0014] The lithium-ion battery lithium plating detection method in this invention is a non-destructive testing method. It involves intermittently applying electrochemical stimulation to a fully charged lithium-ion battery and testing its AC impedance. Based on the change in AC impedance over time, it determines whether metallic lithium has deposited during the charging process. This method is simple and easy to implement, performing non-destructive analysis without disassembling the battery, accurately determining whether lithium plating occurs during charging, and providing a basis for selecting lithium-ion battery charging parameters.

[0015] The detection method in this invention has a wide range of applications and is well-suited for batteries of different models and sizes. The lithium-ion batteries to be tested can be cylindrical, prismatic, soft-pack, aluminum-cased, etc. To ensure the accuracy of the test results and avoid the influence of inherent differences in lithium-ion batteries on the experiment, the lithium-ion batteries to be tested must meet factory requirements. Specifically, the lithium-ion batteries to be tested must be batteries that have undergone formation and capacity testing during the battery manufacturing process, maintaining normal battery condition. Their capacity and internal resistance indicators must meet the factory requirements of the battery manufacturer. The better the battery consistency, the more accurate the test results, and the better they reflect the true situation of lithium deposition within the battery.

[0016] Preferably, the charging process is a constant current charging process.

[0017] Common charging methods for lithium-ion batteries include constant current charging and constant voltage charging. Lithium metal deposition inside the battery typically occurs during the constant current charging stage. Constant voltage charging is a depolarization process; the internal polarization of the battery gradually decreases, the charging current continuously decreases, and the lithium metal deposited on the negative electrode surface is re-embedded into the negative electrode. This invention preferably uses constant current charging, charging the lithium-ion battery to a set state without performing constant voltage charging, thus eliminating the influence of constant voltage charging on the detection results caused by the re-embedding of lithium metal into the negative electrode.

[0018] Furthermore, the charging to the set state refers to charging to a set voltage value or charging to a set SOC value.

[0019] In this invention, the lithium-ion battery is first charged to a set state as a test condition. No special limitations are needed on the set state, i.e., the set cutoff voltage value or the set SOC value, indicating that the detection method of this invention has good applicability. Of course, the set voltage value cannot exceed the battery's fully charged voltage, and the set SOC value cannot exceed 100% to avoid overcharging, which could affect the battery's lifespan and cycle performance, and prevent potential hazards caused by overcharging.

[0020] Furthermore, the charging process, the electrochemical excitation process, and the analysis process are all conducted at the same temperature, and all are under isothermal conditions.

[0021] Furthermore, the temperature error of the constant temperature condition is ±1℃.

[0022] The charging, electrochemical excitation, and analysis processes are all conducted at the same constant temperature to ensure that the measurement results accurately reflect the internal conditions of the lithium-ion battery during charging. Of course, the temperatures mentioned above should be within the range where the battery can operate normally. The temperature difference error under constant temperature conditions is ±1℃ to ensure the accuracy of the measurement results.

[0023] Furthermore, the amplitude of the alternating electrochemical disturbance signal is 20mA and the frequency range is 500mHz-100KHz.

[0024] Furthermore, the interval between the alternating electrochemical perturbation signals is 2-6 minutes.

[0025] Furthermore, the alternating electrochemical perturbation signal is applied 5-10 times.

[0026] The present invention also provides an application method for the above-mentioned non-destructive testing method for lithium plating in lithium-ion batteries, characterized in that: the testing method is applied to determine the charging conditions of lithium-ion batteries under conditions where lithium plating does not occur.

[0027] Furthermore, the charging conditions include the health status of the lithium-ion battery and its temperature environment, charging current, charging cut-off voltage, and state of charge.

[0028] The above testing method is used to determine the charging conditions of lithium-ion batteries without lithium plating. When a specific charging condition needs to be determined, this condition is selected as the variable, while other conditions remain constant. This testing method can determine charging parameters such as the maximum charging current and maximum charging voltage during battery charging, as well as the range of external conditions such as temperature during charging. By determining the charging parameters, rapid charging of the battery can be achieved without affecting battery performance.

[0029] The present invention has the following advantages:

[0030] 1. This invention uses a non-destructive method to detect lithium plating in lithium-ion batteries. The detection method is simple and easy to implement, and the detection results are accurate and objective.

[0031] 2. The testing method in this invention can be used to determine the suitable charging conditions for lithium-ion batteries, providing a basis for the fast charging parameters of lithium-ion batteries.

[0032] 3. The detection method in this invention is highly adaptable and provides accurate test results for different types of lithium-ion batteries. Attached Figure Description

[0033] Figure 1 This is a graph showing the relationship between voltage and time during the charging and discharging process of the lithium-ion battery in this invention.

[0034] Figure 2 This is a graph showing the relationship between current and time during constant-voltage charging of the lithium-ion battery in this invention.

[0035] Figure 3 This is the current-voltage curve during constant current charging in this invention.

[0036] Figure 4 This is a schematic diagram of the alternating current electrochemical disturbance signal in this invention.

[0037] Figure 5 This is the AC impedance spectrum of a lithium-ion battery at a single time point during the analysis process in this invention.

[0038] Figure 6 This is the AC impedance spectrum of the lithium-ion battery when lithium plating did not occur during the analysis process in this invention.

[0039] Figure 7 This is the AC impedance spectrum of a lithium-ion battery when lithium plating occurs during the analysis process in this invention.

[0040] Figure 8 This is the AC impedance spectrum of a lithium-ion battery when lithium plating occurs during the analysis process in this invention.

[0041] Figure 9This is a disassembly diagram showing that the lithium-ion battery in this invention does not undergo lithium plating.

[0042] Figure 10 This is a disassembly diagram of the lithium-ion battery undergoing lithium plating in this invention.

[0043] Figure 11 This is a disassembly diagram of the lithium-ion battery undergoing lithium plating in this invention. Detailed Implementation

[0044] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0045] In this embodiment, the lithium-ion battery to be tested is a 2.15Ah-18650 lithium-ion battery that has been screened.

[0046] The usage process of the lithium-ion battery under test can be simplified to a continuous repetition of charging, resting, and discharging. The voltage-time relationship during the usage process is shown in the attached graph. Figure 1 As shown. During use, lithium metal deposition occurs during battery charging. This embodiment focuses on the charging process of the lithium-ion battery under test.

[0047] The relationship between current and time during the constant voltage charging process of the lithium-ion battery under test is shown in the attached figure. Figure 2 As shown, constant voltage charging is a depolarization process. The polarization inside the battery gradually decreases, the charging current continuously decreases, and the metallic lithium deposited on the negative electrode surface is re-embedded into the battery's negative electrode. In this embodiment, a constant current charging method is used. After the lithium-ion battery under test is charged to a set state with a constant current, constant voltage charging is not performed to eliminate the influence of metallic lithium re-embedding into the battery's negative electrode caused by constant voltage charging on the test results.

[0048] In this embodiment, the lithium-ion battery under test is charged at a constant current of 0.5C, i.e., the charging current is I = 0.5 * 2.15 A = 1075 mA. The charging cutoff voltage is used as a variable, with 4.0V, 4.1V, and 4.2V as the charging cutoff voltages in the experiment. The current-voltage curve during charging at a cutoff voltage of 4.0V is shown in the attached figure. Figure 3 As shown.

[0049] In this embodiment, the charging process, electrochemical excitation process, and analysis process are all conducted at the same temperature, which is kept constant at 10℃, with an error control of ±1℃. After charging to the cutoff voltage, the lithium-ion battery under test is electrochemically excited. During the electrochemical excitation process, the amplitude of the AC electrochemical perturbation signal is 20mA, and the frequency range is 500mHz-100KHz. The AC electrochemical perturbation signal is shown in the attached figure. Figure 4 As shown. The interval between each application of the AC electrochemical perturbation signal was 4 minutes. The AC electrochemical perturbation signal was applied 8 times.

[0050] The AC impedance of the lithium-ion battery was measured after each application of an AC electrochemical perturbation signal (using a Zahner IM6e electrochemical workstation). The AC impedance spectra of the lithium-ion battery at individual time points are attached. Figure 5 As shown in the attached figure, after applying the same perturbation signal to the experimental groups with charging cutoff voltages of 4.0V, 4.1V, and 4.2V respectively, the AC impedance spectra of the lithium-ion batteries under test were obtained. Figure 6-8 As shown, among which, appendix Figure 6 The AC impedance spectrum of the experimental group with a cutoff voltage of 4.0V is attached. Figure 7 The AC impedance spectrum of the experimental group with a cutoff voltage of 4.1V is attached. Figure 8 The AC impedance spectrum is for the experimental group with a cutoff voltage of 4.2V.

[0051] From the appendix Figure 6 It can be seen that the impedance spectrum of the tested lithium-ion battery tends to be uniform, and the impedance arc does not show a step phenomenon from small to large, indicating that no lithium plating occurs inside the tested lithium-ion battery during the charging process with a cutoff voltage of 4.0V. Under these conditions, the tested lithium-ion battery was disassembled to determine the lithium plating situation inside the battery. The disassembly diagram is attached. Figure 9 As shown, by appendix Figure 9 It can be seen that when the cutoff voltage is 4.0V, no lithium plating occurs inside the lithium-ion battery, and the disassembly results are the same as the non-destructive testing results in this embodiment. (See attached...) Figure 7-8 It can be seen that during the charging process with cutoff voltages of 4.1V and 4.2V, the impedance arc in the impedance spectrum of the tested lithium-ion battery exhibited a step-like phenomenon, increasing in size. This indicates that metallic lithium is deposited on the surface of the negative electrode during charging. After charging, the deposited metallic lithium continues to embed into the solid phase of the negative electrode, causing the impedance arc to show a step-like phenomenon with time. Under these conditions, the tested lithium-ion battery was disassembled to determine the lithium deposition situation inside the battery. The disassembly diagram is attached. Figure 10 (Cutoff voltage is 4.1V), attached Figure 11 (The cutoff voltage is 4.2V) As shown, by the attached Figure 10 and attached Figure 11 It can be seen that there is a grayish-white substance on the surface of the negative electrode, which is the result of the reaction after metallic lithium is deposited on the surface of the negative electrode. That is, when the charging cut-off voltage is 4.1V and 4.2V, lithium deposition occurs inside the lithium-ion battery. The disassembly results are the same as the non-destructive testing results in this embodiment. This shows that the non-destructive testing method in this embodiment can accurately reflect the lithium deposition inside the lithium-ion battery.

[0052] To further illustrate the accuracy of the detection method in this embodiment, the number of experimental samples was increased, and the experimental results were analyzed. Specifically, 1000 cells were randomly selected from different batches of 2.15Ah-18650 lithium-ion batteries that met the factory conditions as experimental samples. These samples were divided into five groups of 200 cells each, labeled A, B, C, D, and E. The testing temperature, charging method, electrochemical excitation method, and analysis method were the same as in the previous embodiment. The difference from the previous embodiment was that the charging cutoff voltages for groups A, B, C, D, and E were 3.8V, 3.9V, 4.0V, 4.1V, and 4.2V, respectively. The lithium plating inside the batteries was analyzed using the detection method of this invention, and the results were recorded. Then, all experimental lithium-ion batteries were disassembled, and the lithium plating inside the batteries was statistically analyzed and compared with the results obtained by the detection method of this invention. The comparison results are as follows:

[0053]

[0054] In the table above, the detection rate for non-destructive testing (NDT) is the ratio of the larger of the number of lithium-plated or non-lithium-plated batteries during NDT to the number of experimental samples (200 pcs). The detection rate for disassembly testing is the ratio of the larger of the number of lithium-plated or non-lithium-plated batteries during disassembly testing to the number of experimental samples (200 pcs). As can be seen from the data in the table, the results obtained by the NDT method and the battery disassembly are not significantly different, indicating that the NDT method in this invention can reflect the actual situation of lithium plating inside lithium-ion batteries.

[0055] In summary, the test method in this embodiment can detect whether lithium plating occurs in a lithium-ion battery during charging. To determine other charging parameters of the lithium-ion battery under non-lithium plating conditions, such as charging cut-off voltage, charging current, and charging temperature, simply set the parameters to be determined as variables and use the same method as in this embodiment. That is, this invention is applicable to determining the charging conditions of a lithium-ion battery without lithium plating, determining charging parameters such as maximum charging current and maximum charging voltage during battery charging, and determining the range of external conditions such as temperature during charging. By determining the charging parameters, rapid charging of the battery can be achieved without affecting battery performance.

[0056] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the embodiments of the present invention and not to limit them. Although the embodiments of the present invention have been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the embodiments of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A non-destructive testing method for lithium plating in lithium-ion batteries, characterized in that, Includes the following steps: S01, Charging process: Charge the lithium-ion battery under test to a set state; the charging process is a constant current charging process, and charging to the set state means charging to a set voltage value or charging to a set SOC value. S02, Electrochemical excitation process: After charging is completed, an AC electrochemical perturbation signal is intermittently applied to the lithium-ion battery under test and its AC impedance is monitored; the monitored AC impedance is the AC impedance of the lithium-ion battery after each application of the AC electrochemical perturbation signal. S03, Analysis process: Analyze the relationship between the AC impedance and time. If the AC impedance shows a step change with time, it indicates that lithium plating occurs in the lithium-ion battery under test during the charging process.

2. The non-destructive testing method for lithium plating in lithium-ion batteries as described in claim 1, characterized in that: The charging process, the electrochemical excitation process, and the analysis process are all conducted at the same temperature, and all are under isothermal conditions.

3. The non-destructive testing method for lithium plating in lithium-ion batteries as described in claim 1, characterized in that: The temperature error under the constant temperature conditions is ±1℃.

4. The non-destructive testing method for lithium plating in lithium-ion batteries as described in claim 1, characterized in that: The amplitude of the alternating electrochemical disturbance signal is 20mA and the frequency range is 500mHZ-100KHz.

5. The non-destructive testing method for lithium plating in lithium-ion batteries as described in claim 1, characterized in that: The interval between the alternating electrochemical perturbation signals is 2-6 minutes.

6. The non-destructive testing method for lithium plating in lithium-ion batteries as described in claim 1, characterized in that: The alternating electrochemical perturbation signal is applied 5-10 times.

7. An application method of the non-destructive testing method for lithium plating in lithium-ion batteries as described in any one of claims 1-6, characterized in that: The detection method is used to determine the charging conditions of a lithium-ion battery without lithium plating.

8. The application method of the non-destructive testing method for lithium plating in lithium-ion batteries as described in claim 7, characterized in that: The charging conditions include the health status of the lithium-ion battery and its temperature environment, charging current, charging cut-off voltage, and state of charge.

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