In-situ lithium precipitation detection method based on frequency sweep impedance test

Abstract

The invention discloses an in-situ lithium precipitation detection method based on a sweep frequency impedance test, and the method comprises the steps: carrying out the sweep frequency impedance test through superposing sine AC signals in a specific frequency range and amplitude in a conventional constant current charging process of a lithium ion battery, and achieving the synchronization of the charging process and the impedance test; and judging whether the lithium precipitation behavior of the battery occurs or not by analyzing the change trend of the constant phase element CPE corresponding to the charge transfer impedance. The method provided by the invention has the characteristics of high sensitivity and quick response, can detect the internal state of the battery in real time without damage, and provides online safety early warning for the battery. The composite material is widely applicable to various positive and negative electrode materials and lithium ion batteries under different working conditions, is helpful for improving the safety and stability of the batteries, and particularly has remarkable application potential in high-power charging and extreme environments.

Description

Technical Field

[0001] The present invention relates to the field of electrochemical detection technology, and in particular to an in-situ lithium deposition detection method based on swept frequency impedance testing. Background Art

[0002] With the widespread use of lithium-ion batteries, their safety has become a key research topic. Lithium deposition is a major factor contributing to battery performance degradation and safety risks. This is especially true at high charging voltages, where lithium metal can easily deposit on the negative electrode surface, forming lithium dendrites and increasing battery safety risks.

[0003] In the prior art, the Chinese patent with publication number CN114019385A: lithium plating detection based on the single-frequency impedance method can only be applied under specific conditions. The single-frequency selection of its sinusoidal AC excitation signal has limitations for batteries with different material systems, making it difficult to achieve wide application. In addition, another Chinese patent with publication number CN118625158A uses a triangular wave excitation signal for testing, which is limited to low-rate charge and discharge conditions and difficult to apply in actual working conditions. Therefore, there is an urgent need for a novel and highly adaptable lithium plating detection method that can perform real-time, non-destructive detection under the working state of the battery. Summary of the Invention

[0004] The purpose of the present invention is to provide an in-situ lithium deposition detection method based on swept frequency impedance testing to solve the above defects.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] An in-situ lithium deposition detection method based on swept frequency impedance testing comprises the following steps:

[0007] S1. During the charging process of the lithium-ion battery, a sinusoidal AC signal within a certain frequency range is applied to perform a swept frequency impedance test, wherein the swept frequency impedance test is performed simultaneously with the conventional charging process;

[0008] S2. By analyzing the change trend of the constant phase element CPE corresponding to the charge transfer impedance in the impedance data, especially the sudden change of the CPE value, it is determined whether lithium plating occurs.

[0009] Preferably, in step S1, the frequency range of the swept frequency impedance test is 10kHz to 0.1Hz, but is not limited thereto and can be adjusted according to specific applications. Through the swept frequency impedance test in this frequency range, the changes in charge transfer impedance (Rct) and double layer capacitance (CPE value) caused by lithium deposition can be fully captured, avoiding key information that may be missed by single-frequency testing.

[0010] Preferably, in step S1, the amplitude of the sinusoidal AC signal is 1 / 10 to 1 / 20 of the charging current, but can be adjusted according to actual application. The amplitude range described in the present invention can ensure test accuracy and maximize the signal-to-noise ratio of the impedance signal while minimizing charging interference.

[0011] Preferably, in step S1, data is collected every 5 to 30 seconds during the swept-frequency impedance test, with the specific collection interval set based on the battery characteristics. Setting different data collection intervals achieves an optimal balance between detection accuracy and efficiency, can dynamically adapt to different charging rate requirements, and has been verified to be reliable and practical in practical examples.

[0012] Preferably, in step S1, the positive electrode material of the lithium-ion battery includes lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, or a ternary material, or other materials applicable to lithium-ion batteries. The method of the present invention is applicable to lithium-ion batteries with different positive electrode materials, eliminating the need to search for specific frequencies for different positive electrodes, thereby avoiding interference with the positive electrode impedance characteristics.

[0013] Preferably, in step S1, the negative electrode material of the lithium-ion battery includes graphite, silicon carbon, or other alternative materials suitable for lithium-ion batteries. The method of the present invention is applicable to lithium-ion batteries with different negative electrode materials, demonstrating the universality of the method principle, breaking through the traditional method's reliance on specific negative electrodes, and providing a reliable detection solution for novel negative electrode systems.

[0014] Preferably, in step S2, the judgment of the behavior of the lithium deposition is achieved by drawing a relationship diagram between the CPE value and the charging time, charging capacity or charging state of charge SoC and observing the inflection point of the CPE value. Plot the charging time or charging capacity or charging state of charge SoC with the CPE value, observe the inflection point of the CPE value in the curve, and this point is the starting point of lithium deposition. The principle of the method for judging lithium deposition is based on a given battery system. During the lithium deposition process, the increase in the active area of ​​the negative electrode surface causes a decrease in the impedance of the electrode charge transfer process and an increase in the double-layer capacitance value, which is reflected in the increase in the CPE value. Therefore, according to the image of the curve of the change of the CPE value of the full battery over time, the sudden increase in the CPE value in the figure can be used to judge that lithium deposition has occurred at the negative electrode. The sensitivity is high, and it has the early warning capability of lithium deposition detection. The method is simple and has versatility.

[0015] Preferably, in step S1, the frequency sweep impedance test equipment and charging equipment are implemented by an electrochemical workstation, a superimposed charging and discharging device, or other systems with the same functions. This has the advantages of equipment flexibility and multi-platform compatibility, ultimately achieving synchronization of charging and impedance testing.

[0016] It is ideally suited for a variety of operating conditions, including different operating temperatures and charging rates. It has the advantage of wide temperature adaptability, covering a variety of scenarios including power batteries (high and low temperature environments), energy storage batteries (slow charging), and consumer batteries (fast charging requirements).

[0017] The beneficial effects of the present invention are:

[0018] (1) The present invention provides an in-situ lithium plating detection method based on swept-frequency impedance testing, which combines the DC charging process with the AC swept-frequency impedance detection, and can judge the lithium plating process in real time. There is no need to make three electrodes to find the single frequency corresponding to the negative electrode charge transfer impedance. The value of the constant phase element corresponding to the charge transfer impedance is fitted by the swept-frequency test method to judge whether lithium plating has occurred in the battery cell. It has stronger applicability for lithium plating detection of mass-produced batteries, is simple to operate, and is convenient and reliable.

[0019] (2) The present invention provides an in-situ lithium plating detection method based on swept-frequency impedance testing, which has the characteristics of high sensitivity and rapid response, can detect the internal state of the battery in real time without loss, and provide online safety warning for the battery. It is widely applicable to lithium-ion batteries with various positive and negative electrode materials and different working conditions, and helps to improve the safety and stability of the battery, especially in high-power charging and extreme environments. It has significant application potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 : A charging voltage variation curve of the No. 1 battery of Example 1 under low temperature conditions;

[0021] Figure 2 : A graph showing the impedance variation of the No. 1 battery of Example 1 as a function of SoC when charged under low temperature conditions;

[0022] Figure 3 : A graph showing the change in CPE value of battery No. 1 in Example 1 versus charging SoC;

[0023] Figure 4 : A first-order derivative diagram of the voltage change of the No. 1 battery in Example 1 after being charged and left idle;

[0024] Figure 5 : Comparison diagram of the No. 1 battery frequency sweep method in Example 1 and the prior art single-frequency test method in Example 2;

[0025] Figure 6 : Voltage curve of No. 2 battery in Example 3 under 2.5C constant current constant voltage charging conditions;

[0026] Figure 7 : Spectrum of impedance variation with SoC of No. 2 battery of Example 3 under 2.5C constant current charging condition;

[0027] Figure 8: A graph showing the relationship between the current change value and time during the constant voltage process of the No. 2 battery in Example 3;

[0028] Figure 9 : The relationship between the CPE fitting value and the negative electrode reference potential and SoC of the No. 2 battery in Example 3 during the constant current and constant voltage charging process. DETAILED DESCRIPTION

[0029] The following describes in detail the details of the specific implementation process of the present invention with reference to the accompanying drawings.

[0030] Example 1:

[0031] The present invention provides an in-situ lithium deposition detection method based on swept frequency impedance testing, comprising the following steps:

[0032] S1. During the charging process of the lithium-ion battery, a sinusoidal AC signal within a certain frequency range is applied to perform a swept frequency impedance test. The swept frequency impedance test is performed simultaneously with the conventional charging process.

[0033] The swept-frequency impedance test equipment and charging equipment are implemented using an electrochemical workstation, a superimposed charging and discharging device, or other systems with equivalent functionality. The frequency range of the swept-frequency impedance test is 10kHz to 0.1Hz, but is not limited to this and can be adjusted based on the specific application. During the swept-frequency impedance test, data is collected every 5 to 30 seconds, with the specific collection interval set based on the battery characteristics. The amplitude of the sinusoidal AC signal is 1 / 10 to 1 / 20 of the charging current, but can be adjusted based on the actual application.

[0034] The positive electrode materials of lithium-ion batteries include: lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide or ternary materials or other materials that can be used in lithium-ion batteries. The negative electrode materials of lithium-ion batteries include: graphite, silicon carbon or other alternative materials suitable for lithium-ion batteries.

[0035] S2. By analyzing the change trend of the constant phase element CPE corresponding to the charge transfer impedance in the impedance data, especially the sudden change of the CPE value, it is determined whether lithium plating occurs.

[0036] The judgment of lithium plating behavior is achieved by drawing a relationship graph between the CPE value and the charging time, charging capacity or charging state of charge SoC and observing the inflection point of the CPE value. Plot the CPE value against the charging time or charging capacity or charging state of charge SoC, and observe the inflection point of the CPE value in the curve. This point is the starting point of lithium plating. The principle of the method for judging lithium plating is based on a given battery system. During the lithium plating process, the increase in the active area of ​​the negative electrode surface causes a decrease in the impedance of the electrode charge transfer process and an increase in the double-layer capacitance value, which is reflected in the increase in the CPE value. Therefore, according to the image of the curve of the change of the CPE value of the whole battery over time, the sudden increase in the CPE value in the graph can be used to judge that lithium plating has occurred at the negative electrode. The operation is simple and the accuracy is high.

[0037] The CPE value is related to the charge transfer impedance Rct on the electrode surface and the double-layer capacitance on the electrode surface. When lithium deposition occurs at the negative electrode, the rapid increase in active surface area changes the charge transfer impedance and double-layer capacitance. Therefore, the constant phase element CPE value corresponding to the Rct impedance obtained by fitting the EIS data can reflect the change in the active surface area of ​​the electrode. The inflection point at the starting point of lithium deposition can be used to determine the occurrence of lithium deposition.

[0038] Lithium deposition is determined by plotting the CPE value against charging time, charging capacity, or state of charge. The inflection point of the CPE value in the curve is the starting point of lithium deposition. If the CPE value curve shows a sharp increase, lithium deposition is considered to have occurred at the negative electrode of the battery.

[0039] In this embodiment, the lithium deposition process of battery No. 1 (lithium iron phosphate cylindrical battery, capacity 15Ah) is judged as follows:

[0040] A 15Ah cylindrical battery was used for 1C constant current charging. The test was conducted in a 5°C water bath with a charging voltage range of 2.0V to 3.65V. The impedance test frequency range was 1000Hz to 0.1Hz, the perturbation current was 1.2A, and the impedance test was performed every 30 seconds.

[0041] Lithium plating behavior judgment: The voltage change curve of battery charging is as shown in the attached Figure 1 The impedance spectrum corresponding to the sinusoidal perturbation current applied during the charging process is shown in the attached figure. Figure 2 As shown in the figure, it can be seen that as the charging progresses, the semicircle of the impedance spectrum gradually decreases. According to the theoretical capacity of the battery 15Ah, the 1C current is 15A. When charging the battery with this current, the Figure 4 It can be seen that when the battery is put aside, there is an obvious lithium plating back-insertion platform, indicating that lithium plating has occurred in the battery under low temperature charging conditions. Figure 3As shown in the figure, the CPE value of this battery has an abrupt inflection point at about 87% SoC, corresponding to the increase in electrochemically active surface area caused by lithium plating. At the same time, the inflection point of the CPE value also corresponds to the decrease in the semicircle of the impedance spectrum. Therefore, the inflection point of the CPE value can be used to indicate the occurrence of lithium plating.

[0042] Example 2:

[0043] This embodiment is a comparative example, and adopts a lithium deposition detection method based on single-frequency impedance testing in the prior art (publication number CN114019385A).

[0044] like Figure 5 As shown, the surface capacitance Cs obtained by Example 2 is compared with the CPE value used in Example 1, and the single frequency used in the comparative example is 10 Hz. It can be seen that both the single frequency and swept frequency testing methods can obtain the time point when lithium precipitation occurs, and the capacitance values ​​obtained by the two methods are in the same order of magnitude, and the turning point is around 87% SoC. Therefore, the effectiveness and convenience of this method are demonstrated.

[0045] However, the Chinese patent publication number CN114019385A in Example 2: A lithium plating detection method based on single-frequency impedance testing, which uses a single-frequency method, requires a three-electrode test to find the single-frequency frequency corresponding to the negative electrode charge transfer impedance, and avoids the single-frequency frequency from coinciding with the characteristic frequency of the positive electrode charge transfer impedance, in order to effectively detect the lithium plating process of the battery, which has certain limitations. In Example 1, the method of the present invention adopts a method of sweeping the frequency impedance within a certain frequency range. By fitting the electrochemical impedance spectrum obtained by the test with an equivalent circuit, the value of the constant phase element CPE corresponding to the charge transfer impedance and its change trend are obtained, thereby judging whether lithium plating has occurred in the battery. It can be directly applied to the whole battery without finding a characteristic single-frequency frequency.

[0046] Example 3:

[0047] The specific steps of the in-situ lithium deposition detection method based on swept frequency impedance testing of the present invention are basically the same as those of the embodiment, except that:

[0048] In this embodiment, the lithium deposition process of a No. 2 battery (lithium iron phosphate square battery, capacity 100Ah) is judged as follows:

[0049] A 100Ah prismatic battery was used for 2.5C constant current and constant voltage charging. The test was conducted in a 25°C water bath with a charging voltage range of 2.0V to 3.65V. The impedance test frequency range was 1000Hz to 0.1Hz, with a perturbation current of 12.25A and an impedance test interval of 30 seconds.

[0050] Lithium plating behavior judgment: The voltage change curve of the battery constant current constant voltage charging is as shown in the attached Figure 6 The impedance spectrum corresponding to the sinusoidal perturbation current applied during the charging process is shown in the attached figure. Figure 7 As shown in the figure, it can be seen that as the charging progresses, the semicircle of the impedance spectrum gradually shifts to the left, and the diameter of the semicircle also changes. According to the theoretical capacity of the battery 100Ah, the 2.5C current is 245A. When charging the battery with this current, the Figure 8 It can be seen that when the battery is at constant voltage, there is an obvious current peak of lithium plating back, indicating that lithium plating occurs in the battery at this charging rate. Figure 9 As shown in the figure, the CPE value of the battery has a sudden inflection point at around 44% SoC, and the potential of the negative electrode to the reference drops below 0V at 44% SoC, which corresponds to the occurrence of lithium plating. Since the test scheme adopted is a constant current and constant voltage charging mode, the battery current continues to decrease during the constant voltage. The current reduction may not cause the recurrence of lithium plating, so the frequency sweep impedance monitoring was not performed during the constant voltage stage. See the attached Figure 9 As shown, attached Figure 6 The mid-charge voltage curve can also show the constant voltage stage without frequency sweep impedance monitoring. Figure 9 The growth rate of the CPE value before 44% SoC is greater than the growth rate of the CPE value after 44% SoC. The reason may be that lithium precipitation includes two stages: lithium nucleation and dendrite growth, and the surface area of ​​the lithium nucleation stage is larger, which leads to a faster growth of the CPE value before 44% SoC.

[0051] This embodiment verifies the accuracy and convenience of the swept-frequency impedance test method. There is no need to find a characteristic single-frequency. It is only necessary to fit the impedance spectrum obtained during the swept-frequency process to obtain the constant phase element CPE value corresponding to the charge transfer impedance. By observing the trend of the CPE value change, it can be determined whether lithium plating has occurred in the battery.

[0052] The present invention provides an in-situ lithium deposition detection method based on swept-frequency impedance testing, which is applicable to a variety of operating conditions, including different operating temperatures and charging rates. The method has a wide range of applications and can be performed under different operating temperatures and charging rates. It has the advantage of adaptability over a wide temperature range, covering a variety of scenarios, including power batteries (high and low temperature environments), energy storage batteries (slow charging), and consumer batteries (fast charging requirements).

[0053] The present invention provides an in-situ lithium plating detection method based on swept-frequency impedance testing, which combines a DC charging process with an AC swept-frequency impedance detection, and can judge the lithium plating process in real time. There is no need to make three electrodes to find the single frequency corresponding to the negative electrode charge transfer impedance. The value of the constant phase element corresponding to the charge transfer impedance is fitted by the swept-frequency test method to judge whether lithium plating has occurred in the battery cell. The method has stronger applicability for lithium plating detection of mass-produced batteries, is simple to operate, and is convenient and reliable.

[0054] The present invention provides an in-situ lithium plating detection method based on swept-frequency impedance testing, which has the characteristics of high sensitivity and rapid response, can non-destructively detect the internal state of the battery in real time, and provide online safety warnings for the battery. The method is widely applicable to lithium-ion batteries with various positive and negative electrode materials and different operating conditions, and helps to improve the safety and stability of the battery. In particular, it has significant application potential in high-power charging and extreme environments.

[0055] The above description of the invention is illustrative in combination with the accompanying drawings. It is obvious that the specific implementation of the present invention is not limited to the above-mentioned method. As long as such non-substantial improvements are made using the method concept and technical solution of the present invention, or the concept and technical solution of the invention are directly applied to other occasions without improvement, they are all within the scope of protection of the present invention.

Claims

1. An in-situ lithium deposition detection method based on swept frequency impedance testing, characterized in that: The following steps are involved: S1. During the charging process of the lithium-ion battery, a sinusoidal AC signal within a certain frequency range is applied to perform a swept frequency impedance test, wherein the swept frequency impedance test is performed simultaneously with the conventional charging process; S2. By analyzing the change trend of the constant phase element CPE corresponding to the charge transfer impedance in the impedance data, especially the sudden change of the CPE value, it is determined whether lithium plating occurs.

2. The in-situ lithium deposition detection method based on swept frequency impedance testing according to claim 1, characterized in that: In step S1, the frequency range of the swept frequency impedance test is 10 kHz to 0.1 Hz.

3. The in-situ lithium deposition detection method based on swept frequency impedance testing according to claim 1, characterized in that: In step S1 , the amplitude of the sinusoidal AC signal is 1 / 10 to 1 / 20 of the charging current.

4. The in-situ lithium deposition detection method based on swept frequency impedance testing according to claim 1, characterized in that: In step S1, data is collected every 5 to 30 seconds during the swept frequency impedance test.

5. The in-situ lithium deposition detection method based on swept frequency impedance testing according to claim 1, characterized in that: In step S1, the positive electrode material of the lithium-ion battery includes: lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide or a ternary material.

6. The in-situ lithium deposition detection method based on swept frequency impedance testing according to claim 1, characterized in that: In step S1, the negative electrode material of the lithium-ion battery includes: graphite and silicon carbon.

7. The in-situ lithium deposition detection method based on swept frequency impedance testing according to claim 1, characterized in that: In step S2, the lithium plating behavior is determined by plotting a relationship between the CPE value and the charging time, charging capacity or charging state of charge (SoC) and observing the inflection point of the CPE value.

8. The in-situ lithium deposition detection method based on swept frequency impedance testing according to claim 1, characterized in that: In step S1, the frequency sweep impedance test equipment and charging equipment are implemented by an electrochemical workstation and a superimposed charging and discharging device.

9. The in-situ lithium deposition detection method based on swept frequency impedance testing according to claim 1, characterized in that: Applicable to working conditions with different operating temperatures and different charging rates.

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