A method for obtaining a lithium precipitation window of a lithium ion battery

Abstract

The application discloses a lithium ion battery lithium precipitation window acquisition method, steps comprising: charging a three-electrode lithium ion battery in a non-full discharge state at temperature T, superimposing a sinusoidal disturbance current on the charging current, and confirming the optimal sinusoidal disturbance current; superimposing the optimal sinusoidal disturbance current on the charging current, measuring the electrochemical impedance spectrum between the negative electrode and the reference electrode, and defining the frequency corresponding to the maximum value of the negative electrode imaginary impedance as the characteristic frequency; changing the charging rate and the test temperature under the single-frequency current disturbance of the characteristic frequency f respectively for charging test, obtaining the SOC-negative electrode imaginary impedance curve; determining the imaginary impedance inflection point in the curve as the lithium precipitation starting point, recording the corresponding lithium precipitation SOC, and obtaining the lithium precipitation window. Through dynamic impedance test on a small three-electrode laminated structure battery cell, the influence of temperature on the battery impedance is excluded by using the temperature rise of the small battery cell itself, and the positive and negative electrode impedance signals are distinguished by the three electrodes, so that the negative electrode impedance change under different temperature and rate charging states is recorded.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically a method for obtaining the lithium plating window of a lithium-ion battery. Background Technology

[0002] Under conditions of low temperature, high rate, or overcharge, lithium-ion batteries are prone to lithium plating on the graphite surface of the negative electrode, leading to capacity decay and potential safety hazards. Accurately determining the lithium plating window of the battery at different temperatures and rates is crucial for developing fast-charging strategies and ensuring battery safety.

[0003] For high-power batteries, fast charging capability is a crucial indicator of battery competitiveness. Currently, assessing the lithium plating window of high-power batteries is challenging. Traditional methods involve disassembling the cell under a specific fast-charging regime and determining the presence of lithium plating at the negative electrode interface. Another method involves assembling a three-electrode system and determining cell capability by detecting changes in the negative electrode potential at different charging rates. The first method primarily assesses the fast-charging regime through the cell interface but cannot detect the onset of lithium plating. The second method, when applied to high-power batteries, may face the problem of excessive overpotential at high rates, resulting in a narrow lithium plating window determined by potential alone. Other lithium plating testing methods mainly characterize batteries with significant lithium plating but are not particularly effective for those with slight lithium plating. Currently, the main method for detecting slight lithium plating is impedance testing. However, high-power product-grade cells are usually tested at very high rates and at high temperatures. The correlation between impedance and temperature is too strong, and the impedance changes and contributions of the positive and negative electrodes are often difficult to distinguish. Therefore, impedance testing is also difficult to determine the charging window of high-power cells. Therefore, there is an urgent need in the field for a test method that can accurately, continuously, and online detect the lithium plating window of graphite anodes, especially suitable for power batteries with high-rate charging. Summary of the Invention

[0004] In view of this, the present invention provides a method for obtaining the lithium plating window of a lithium-ion battery. By analyzing the dynamic impedance of the three electrodes, the method continuously monitors the change in the imaginary part impedance of the negative electrode during charging, which can accurately, quickly and non-destructively determine the lithium plating initiation point and lithium plating window of a graphite negative electrode power battery at different temperatures and different rates, providing a basis for the formulation of fast charging strategies.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: This invention discloses a method for obtaining the lithium plating window of a lithium-ion battery, comprising the following steps: S1. At temperature T, charge a non-fully discharged three-electrode lithium-ion battery and add a sinusoidal perturbation current to the charging current. Determine the optimal sinusoidal perturbation current I based on the quality of low- and medium-frequency data. S2. Superimpose the optimal sinusoidal perturbation current I onto the charging current, measure the electrochemical impedance spectrum between the negative electrode and the reference electrode, and define the frequency corresponding to the maximum value of the imaginary part impedance of the negative electrode as the characteristic frequency f. S3. Under the single-frequency current disturbance at the characteristic frequency f, the charging rate C and the test temperature T are changed respectively to carry out the charging test and obtain the SOC-negative electrode imaginary part impedance curve. S4. Determine the inflection point of the imaginary impedance in the SOC-negative electrode imaginary impedance curve as the starting point of lithium deposition, record the corresponding lithium deposition SOC, and obtain the lithium deposition window at different temperatures T and rate C.

[0006] Current methods for evaluating the lithium plating window in high-power battery systems are difficult to implement, especially for detecting slight lithium plating. Commonly used testing methods cannot accurately define the onset point of lithium plating. This invention uses dynamic impedance testing on small three-electrode stacked cells. On the one hand, it utilizes the fact that the small cell itself has no temperature rise to eliminate the influence of temperature on battery impedance. On the other hand, it uses the three electrodes to distinguish the positive and negative impedance signals, recording the change of negative electrode impedance under different temperatures and charging rates, thereby defining the cell charging boundary.

[0007] Steps S1 and S2 dynamically determine the optimal perturbation current and characteristic frequency using a three-electrode system, solving the problem of poor adaptability to fixed frequencies in existing technologies. Step S3 obtains the negative electrode SOC-imaginary impedance curve through variable rate and temperature testing, enabling system evaluation under different operating conditions. Step S4 determines the lithium plating initiation SOC by inflection point identification, ultimately outputting the lithium plating window at different temperatures and rates. This method does not require interrupting charging, enables continuous online monitoring, and provides intuitive output results that can be directly used to guide fast charging strategy development.

[0008] As a further aspect of the present invention, the non-fully discharged state mentioned in step S1 specifically refers to the battery's initial state of charge being greater than 15% SOC. Limiting the battery's initial state of charge to greater than 15% SOC avoids the problem of a large rate of change in characteristic frequency under low lithium intercalation states, ensuring the accuracy of the characteristic frequency f and the reliability of subsequent tests.

[0009] As a further aspect of this invention: the step S1, which involves determining the optimal sinusoidal perturbation current I based on the quality of low- and mid-frequency data, specifically involves determining the I value at different temperatures T based on the integrity of the negative electrode charge transfer impedance arc and the test linearity conditions. The I value must simultaneously satisfy the condition that the excitation signal does not cause nonlinear distortion. Determining the optimal perturbation current I by considering the integrity and linearity of the negative electrode charge transfer impedance arc ensures that the excitation signal does not cause nonlinear distortion, thereby obtaining high-quality, repeatable impedance data. This provides a data foundation for subsequent characteristic frequency determination and lithium plating criterion identification.

[0010] As a further aspect of the present invention, the measurement of the electrochemical impedance spectroscopy between the negative electrode and the reference electrode in step S2 specifically involves: maintaining a constant charging current during charging, superimposing the optimal sinusoidal perturbation current I, and scanning a frequency range of 1 mHz to 1 kHz to obtain impedance data of the negative electrode at different frequencies. Maintaining a constant current and superimposing a perturbation current during charging, while scanning a wide frequency range of 1 mHz to 1 kHz, allows for comprehensive acquisition of impedance data of the negative electrode at different frequencies, covering complete kinetic information from ion transport, charge transfer, and diffusion processes, providing data support for accurate identification of characteristic frequencies.

[0011] As a further aspect of the present invention: the frequency corresponding to the maximum value of the imaginary impedance of the negative electrode in step S2 is defined as the characteristic frequency f. Specifically, during the charging process, a sinusoidal perturbation current is superimposed, and the electrochemical impedance spectrum between the negative electrode and the reference electrode is collected. The imaginary maximum point at the top of the charge transfer arc in the impedance spectrum is identified, and the frequency corresponding to this maximum point is the characteristic frequency f. By identifying the imaginary maximum point at the top of the charge transfer arc to determine the characteristic frequency f, the characteristic frequency can dynamically reflect the electrochemical characteristics of the current battery system. This differs from the fixed frequency approach in the prior art, improving the sensitivity and adaptability of subsequent single-frequency testing for lithium plating detection.

[0012] As a further aspect of the present invention, step S3 specifically involves: continuously applying a single-frequency sinusoidal current disturbance with a frequency of f and an amplitude of the optimal sinusoidal disturbance current I during the charging process; acquiring the response voltage signal between the negative electrode and the reference electrode in real time; calculating the change in the imaginary impedance of the negative electrode with charging time; and converting the charging time into a state of charge. By continuously applying a single-frequency sinusoidal current disturbance during the charging process, acquiring the response voltage signal in real time, and calculating the imaginary impedance, continuous and online monitoring during the charging process is achieved without interrupting charging, thus avoiding the shortcomings of the charging-restoration method in the prior art, which cannot continuously monitor the process.

[0013] As a further aspect of the present invention: the charging test performed by changing the charging rate C in step S3 specifically involves conducting independent constant current charging tests at at least three different rates selected from 0.1C, 0.5C, 1C, 2C, 3C, 5C, and 10C at a fixed temperature T. Each rate test uses an independent three-electrode lithium-ion battery. By conducting independent tests at at least three different rates at a fixed temperature, the impact of the charging rate on the initial state of lithium plating (SOC) can be systematically evaluated, the lithium plating boundary at different charging rates can be clarified, and a quantitative basis can be provided for rate selection in fast charging strategies.

[0014] As a further aspect of the present invention: the charging test performed by changing the test temperature T in step S3 specifically involves conducting independent constant current charging tests at at least three different temperatures selected from -10℃, 0℃, 10℃, 25℃, and 45℃ under a fixed charging rate C. Each temperature test uses an independent three-electrode lithium-ion battery. By conducting independent tests at at least three different temperatures under a fixed charging rate, the influence of temperature on the initial state of lithium plating (SOC) can be systematically evaluated, the risk boundary of lithium plating under harsh conditions such as low temperatures can be clarified, and guidance can be provided for the battery's operating temperature range.

[0015] As a further aspect of this invention: the inflection point of the imaginary impedance mentioned in step S4 is specifically defined as follows: when the State of Charge (SOC) reaches a certain critical value, the imaginary impedance changes from a slow decrease to a rapid decrease. This transition point is the inflection point of the imaginary impedance, corresponding to the initial SOC of lithium plating. That is, in the SOC-negative electrode imaginary impedance curve, the point where the first derivative of the imaginary impedance with respect to SOC is negative and has the smallest value corresponds to the initial SOC of lithium plating. By clearly defining the inflection point where the imaginary impedance changes from a slow decrease to a rapid decrease as the starting point of lithium plating, the impedance characteristic differences between the normal lithium intercalation process and the lithium plating process are distinguished, providing a clear and quantifiable criterion for the automatic identification of the initial SOC of lithium plating, and avoiding errors caused by subjective judgment.

[0016] As a further aspect of the present invention: the lithium plating window is a set of lithium plating start-up SOCs corresponding to different test temperatures T and different charging rates C.

[0017] Compared with the prior art, the beneficial effects of the present invention are: The small-cell stacked structure used in this invention exhibits almost no temperature rise during charging, eliminating the influence of temperature on impedance changes. The three-electrode system directly measures the imaginary part impedance of the negative electrode, eliminating interference from positive electrode impedance changes and resulting in higher detection accuracy. By dynamically determining the characteristic frequency f, it replaces the fixed-frequency approach in existing technologies, adapting to different battery systems and operating conditions, and significantly improving detection sensitivity. The continuous single-frequency perturbation method shortens the test step size compared to full-frequency methods, making the determination of the lithium plating inflection point more accurate. The test does not require interruption of charging, enabling continuous online monitoring during the charging process.

[0018] Furthermore, this invention addresses the problem of impedance spectrum distortion causing traditional criteria to fail under high-rate charging of power batteries by proposing a modified criterion, thus expanding the applicability of the method. Through systematic variable rate and variable temperature testing, a temperature-rate-lithium plating SOC window can be output, comprehensively evaluating the lithium plating boundary of the battery. This provides a direct basis for the formulation of fast charging strategies, effectively reducing the risk of lithium plating and extending battery life. Attached Figure Description

[0019] Figure 1This is the negative electrode static impedance spectrum of the Ni65 three-electrode small stack in the embodiment of the present invention, used to determine the characteristic frequency f; Figure 2 The full-frequency dynamic impedance spectrum of the negative electrode of the Ni65 three-electrode small stacked cell in the embodiment of the present invention at a state of charge (SOC) of 0~20%; Figure 3 The full-frequency dynamic impedance spectrum of the negative electrode of the Ni65 three-electrode small stacked cell in the embodiment of the present invention at a state of charge (SOC) of 20~40%; Figure 4 The full-frequency dynamic impedance spectrum of the negative electrode of the Ni65 three-electrode small stacked cell in the embodiment of the present invention at a state of charge (SOC) of 40~60%; Figure 5 The negative electrode single-frequency dynamic impedance spectrum of the Ni65 three-electrode small stacked battery in this embodiment of the invention shows the variation curve of the imaginary impedance with SOC at different charging rates, which is used to determine the lithium plating window. Detailed Implementation

[0020] To facilitate understanding of the present invention, a more comprehensive description will be given below with reference to specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0022] In this embodiment, the fabrication of a three-electrode stacked cell for a Ni65 high-power system is completed, specifically: Cathode preparation: The cathode active material LiNi is prepared... 0.65 Co 0.15 Mn 0.2 O2, conductive agent Super P, and binder PVDF are mixed in a mass ratio of 97.5:1.5:1, NMP solvent is added and stirred evenly, and the mixture is coated onto a 12μm aluminum foil. After drying and rolling, a positive electrode sheet is obtained with a single-sided areal density of 157 g / m². 2 The compacted density is 3.52 g / cm³. 3 .

[0023] Negative electrode preparation: Artificial graphite, conductive agent Super P, binder SBR, and thickener CMC are mixed in a mass ratio of 96.7:0.7:1.4:1.2. Deionized water is added and stirred evenly. The mixture is then coated onto a 6μm copper foil. After drying and rolling, the negative electrode sheet is obtained, with a single-sided areal density of 100 g / m². 2 The compacted density is 1.6 g / cm³. 3 The N / P ratio is 1.13.

[0024] Reference electrode preparation: Take a copper wire with a diameter of 0.05 mm, cut it to a length of about 30 cm, and remove about 2 cm of enameled wire from one end with paint remover to obtain the reference electrode.

[0025] Battery assembly: The positive electrode, separator (PP / PE / PP three-layer separator, 17μm thick), reference electrode, separator, and negative electrode are stacked in sequence. The reference electrode is placed between the positive and negative electrodes without contacting them. Electrolyte is added dropwise with an injection coefficient of 2.5g / Ah. The battery is then packaged into a small pouch cell, which undergoes 0.1C formation, degassing, secondary injection, and sealing. The other end of the reference electrode is led out through the tin-soldering structure of a copper-nickel tab sheet, resulting in a three-electrode stacked battery.

[0026] The three-electrode stacked cell of this Ni65 high-power system was tested according to the following steps: S1. Determine the optimal sinusoidal disturbance current I A three-electrode stacked battery with a 50% state of charge (SOC) was charged at T=25℃, with a charging rate of 1C. A sinusoidal perturbation current was superimposed on the charging current, with the amplitude of the perturbation current gradually increasing from 0.01C to 0.2C. Simultaneously, the electrochemical impedance spectroscopy between the negative electrode and the reference electrode was monitored to observe the integrity of the charge transfer impedance arc in the low-to-mid-frequency region. When the perturbation current was too small, the impedance signal-to-noise ratio was insufficient; when the perturbation current was too large, the impedance spectrum exhibited nonlinear distortion. Through testing, the optimal sinusoidal perturbation current I=0.1C was determined at T=25℃ in this embodiment. Similarly, I=0.04C was determined at T=0℃, and I=0.2C was determined at T=45℃.

[0027] S2. Determine the characteristic frequency f The battery was charged at a temperature of T=25℃ and a state of charge of 50% (SOC) with a charging rate of 1C. An optimal sinusoidal perturbation current of I=0.1C, determined by S1, was superimposed on the charging current. The electrochemical impedance spectroscopy between the negative electrode and the reference electrode was scanned in the full frequency domain from 1 mHz to 1 kHz using an electrochemical workstation. Figure 1 This is the static impedance spectrum of the negative electrode measured in this embodiment. (From...) Figure 1It can be seen that there is an imaginary maximum point at the top of the charge transfer arc in the mid-frequency region of the impedance spectrum. The frequency corresponding to this point is 120Hz, which is defined as the characteristic frequency f.

[0028] S3, variable rate and variable temperature charging tests were performed to obtain the SOC-negative electrode imaginary part impedance curve. During charging, a single-frequency sinusoidal current disturbance with a frequency of f=120Hz and an amplitude of I=0.1C is continuously applied. The response voltage signal between the negative electrode and the reference electrode is acquired in real time. The change in the imaginary part impedance of the negative electrode with charging time is calculated, and the charging time is converted into a state of charge. Tests with varying charging rate C and varying test temperature T are performed respectively.

[0029] (1) Variable rate test: At a temperature of T=25℃, independent constant current charging tests were conducted at at least three different rates of 0.1C, 0.5C, 1C, 2C, 3C, 5C and 10C. Each rate test used an independent three-electrode battery. In each rate test, a single frequency current disturbance was applied in the manner described above and the SOC-negative electrode imaginary part impedance curve was recorded.

[0030] (2) Variable temperature test: Under a fixed charging rate C=1C, independent constant current charging tests were conducted at at least three different temperatures of -10℃, 0℃, 10℃, 25℃ and 45℃. Each temperature test used an independent three-electrode battery. In each temperature test, a single-frequency current disturbance was applied in the manner described above and the SOC-negative electrode imaginary part impedance curve was recorded.

[0031] Please see Figure 2 This study demonstrates the full-frequency dynamic impedance spectrum during the initial charging phase (0-20% SOC). After applying the charging current, full-frequency testing was performed simultaneously with the charging process. The electrochemical impedance spectrum initially exhibited a contraction and deformation process across the entire spectrum. The contraction was due to the increased active surface area caused by initial graphite phase changes and increased thickness, leading to a sharp decrease in electrochemical impedance. The deformation primarily occurred in high-current tests of the high-rate system, manifested as an increase in both the imaginary and real impedances at a fixed frequency. In contrast, in typical static AC impedance testing, the impedance of the graphite anode system usually remains constant or decreases slowly with increasing SOC. The combined effect of these two factors resulted in impedance spectrum deformation in the high-current test of the high-rate system.

[0032] Please continue reading. Figure 3The diagram illustrates the process by which the impedance spectrum changes from deformation to a sharp decrease within the 20-40% SOC range, clearly indicating the lithium plating initiation point. During the T25-5C charging process, as the SOC increases from 28-32% to 32-36%, the impedance spectrum changes from a deformation process to a sharp decrease. The reason for this is that the change in the imaginary impedance during the second process is related to the lithium plating process. The deposited lithium provides additional electrochemical reaction sites and an electric double layer, leading to a rapid decrease in the imaginary impedance. This SOC point is the lithium plating initiation point defined in this invention.

[0033] Please continue reading. Figure 4 This study demonstrates the phenomenon that the imaginary impedance continuously decreases while the real impedance does not maintain a decreasing trend during the lithium plating process within the 40-60% SOC range. During the rapid decrease in impedance spectrum, the imaginary impedance is closely related to the electrochemical reaction sites; therefore, it shows a continuous decreasing trend with the progress of lithium plating. However, the real impedance does not maintain a decreasing trend with the lithium plating process. Therefore, the discrimination signal of the test method of this invention is always provided by the imaginary impedance.

[0034] S4. Determine the lithium plating initiation point and obtain the lithium plating window. The inflection point of the imaginary impedance in the SOC-negative electrode imaginary impedance curve is determined as the starting point of lithium deposition, and the corresponding lithium deposition SOC is recorded.

[0035] Definition of inflection point: In the SOC-imaginary impedance curve of the negative electrode, as SOC increases, the imaginary impedance first shows a slow decreasing trend, which is related to the change of the graphite lithium intercalation phase; when SOC reaches a certain critical value, the imaginary impedance changes from a slow decreasing to a rapid decreasing, and this turning point is the inflection point of the imaginary impedance, corresponding to the SOC at which lithium plating begins.

[0036] In general: the point where the imaginary impedance first shows a rapid decrease is determined as the lithium plating initiation point, such as... Figure 3 As shown.

[0037] Special case at high rates: When the imaginary impedance at the characteristic frequency increases instead of decreases due to the sharp deformation of the electrochemical impedance spectrum under high-rate charging conditions, the point where the imaginary impedance changes from increasing to decreasing and the rate of decrease does not increase again is determined as the lithium plating initiation point.

[0038] Please continue reading. Figure 5This invention performs single-frequency testing at a fixed characteristic frequency (120Hz under this test condition). Based on the inflection point of the imaginary impedance at different rates, it evaluates the lithium plating window of the cell at different temperatures and rates. The inflection point where the imaginary impedance decreases sharply is the lithium plating starting point defined by this invention. Signals where the imaginary impedance increases instead of decreasing due to system or rate can be ignored. In addition, due to the fast single-frequency scanning speed, the problems caused by excessively large step sizes in full-frequency domain scanning are avoided (e.g., a step size change of 4% SOC within the 600Hz~30Hz frequency band under 5C testing).

[0039] The initial state of lithium plating (SOC) at different test temperatures (T) and charging rates (C) was statistically analyzed to form a matrix representing the temperature-rate-SOC relationship of the battery cell. This matrix represents the lithium plating window of the battery cell. The partial lithium plating window data measured in this embodiment are shown in Table 1.

[0040] It should be noted that the lithium plating window mentioned in this invention refers to the set of critical SOC values ​​at which the graphite anode begins to undergo lithium plating reaction at different temperatures and charging rates, obtained through three-electrode dynamic impedance analysis. It is expressed as a correspondence between temperature, charging rate, and lithium plating SOC.

[0041] Table 1

[0042] As shown in Table 1, charging tests were conducted at T=25℃ using 3C, 4C, 5C, 6C, and 7C rates. The initial state of lithium plating (SOC) measured by the method of this invention (dynamic impedance method) was compared with that measured by the traditional method (negative electrode potential method). The results show that the initial SOC of lithium plating measured by the method of this invention is higher than that measured by the negative electrode potential method, with a difference between 15 and 27 percentage points. This indicates that the method of this invention is more sensitive to lithium plating detection, providing greater redundancy for timely adjustment of the charging strategy.

[0043] Although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0044] Therefore, the above description is only a preferred embodiment of this application and is not intended to limit the scope of this application; that is, all equivalent modifications made in accordance with the scope of the claims of this application shall be within the protection scope of the claims of this application.

Claims

1. A method for obtaining the lithium plating window of a lithium-ion battery, characterized in that, Includes the following steps, S1. At temperature T, charge a non-fully discharged three-electrode lithium-ion battery and add a sinusoidal perturbation current to the charging current. Determine the optimal sinusoidal perturbation current I based on the quality of low- and medium-frequency data. S2. Superimpose the optimal sinusoidal perturbation current I onto the charging current, measure the electrochemical impedance spectrum between the negative electrode and the reference electrode, and define the frequency corresponding to the maximum value of the imaginary part impedance of the negative electrode as the characteristic frequency f. S3. Under the single-frequency current disturbance at the characteristic frequency f, the charging rate C and the test temperature T are changed respectively to carry out the charging test and obtain the SOC-negative electrode imaginary part impedance curve. S4. Determine the inflection point of the imaginary impedance in the SOC-negative electrode imaginary impedance curve as the starting point of lithium deposition, record the corresponding lithium deposition SOC, and obtain the lithium deposition window at different temperatures T and rate C.

2. The method according to claim 1, characterized in that, The non-fully discharged state mentioned in step S1 specifically refers to the battery's initial state of charge being greater than 15% SOC and less than 80% SOC.

3. The method according to claim 1, characterized in that, The step S1, which involves determining the optimal sinusoidal disturbance current I based on the quality of low- and medium-frequency data, specifically involves determining the I value at different temperatures T based on the integrity of the negative electrode charge transfer impedance arc and the test linearity conditions. The I value must simultaneously satisfy the condition that the excitation signal does not cause nonlinear distortion.

4. The method according to claim 1, characterized in that, The measurement of the electrochemical impedance spectrum between the negative electrode and the reference electrode in step S2 specifically involves: maintaining a constant charging current during the charging process, superimposing the optimal sinusoidal perturbation current I, and scanning a frequency range of 1 mHz to 1 kHz to obtain the complex impedance data of the negative electrode at different frequencies.

5. The method according to claim 1, characterized in that, In step S2, the frequency corresponding to the maximum value of the imaginary impedance of the negative electrode is defined as the characteristic frequency f. Specifically, during the charging process, the electrochemical impedance spectrum between the negative electrode and the reference electrode is scanned in the full frequency domain to identify the maximum value point of the imaginary part at the top of the charge transfer arc in the impedance spectrum. The frequency corresponding to this maximum value point is the characteristic frequency f.

6. The method according to claim 1, characterized in that, Step S3 specifically involves: continuously applying a single-frequency sinusoidal current disturbance with a frequency of f and an amplitude of the optimal sinusoidal disturbance current I during the charging process, acquiring the response voltage signal between the negative electrode and the reference electrode in real time, calculating the change data of the imaginary part impedance of the negative electrode with charging time, and converting the charging time into a state of charge.

7. The method according to claim 1, characterized in that, The charging test with varying charging rate C mentioned in step S3 specifically involves conducting independent constant current charging tests at at least three different rates selected from 0.1C, 0.5C, 1C, 2C, 3C, 5C, and 10C at a fixed temperature T. Each rate test uses an independent three-electrode lithium-ion battery.

8. The method according to claim 1, characterized in that, The charging test described in step S3 by changing the test temperature T is specifically as follows: under a fixed charging rate C, independent constant current charging tests are performed at at least three different temperatures, namely -10℃, 0℃, 10℃, 25℃, and 45℃, with each temperature test using an independent three-electrode lithium-ion battery.

9. The method according to claim 1, characterized in that, The inflection point of the imaginary impedance mentioned in step S4 is specifically the point in the SOC-negative electrode imaginary impedance curve where the first derivative of the imaginary impedance with respect to SOC is negative and has the smallest value. This point corresponds to the initial SOC of lithium plating.

10. The method according to claim 1, characterized in that, The lithium plating window is a set of lithium plating start-up states (SOCs) corresponding to different test temperatures (T) and different charging rates (C).

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