A lithium battery overcharge and overdischarge detection method based on electrochemical impedance spectroscopy

Abstract

The present disclosure discloses a lithium battery overcharge and overdischarge detection method based on electrochemical impedance spectroscopy, comprising: constructing an equivalent circuit model of a lithium battery; measuring the electrochemical impedance spectrum of a new lithium battery under standard charge and discharge, and identifying the parameters of each device in the equivalent circuit model to obtain the fitting index and equivalent capacitance of the new lithium battery under standard charge and discharge; measuring the electrochemical impedance spectrum of the lithium battery to be tested after a certain number of charge and discharge cycles, and identifying the parameters of each device in the equivalent circuit model to obtain the fitting index and equivalent capacitance of the lithium battery to be tested after a certain number of charge and discharge cycles; comparing the fitting index of the lithium battery to be tested with the fitting index of the new lithium battery to determine whether the lithium battery to be tested is in overdischarge state; comparing the equivalent capacitance of the lithium battery to be tested with the equivalent capacitance of the new lithium battery to determine whether the lithium battery to be tested is in overcharge state.

Description

Technical Field

[0001] This disclosure pertains to the field of lithium battery testing, specifically relating to a method for detecting overcharge and over-discharge of lithium batteries based on electrochemical impedance spectroscopy. Background Technology

[0002] Lithium-ion single-cell batteries cannot meet the high voltage, high current, and high power requirements of drive motors in electric vehicles. Different series and parallel configurations of individual cells are needed to combine them to achieve the required high voltage and high current. Since battery capacity, internal resistance, and other parameters cannot be uniform during production, inconsistencies exist between individual cells. These differences can lead to overcharging and over-discharging of smaller cells. While overcharging and over-discharging of individual cells in the initial cycle count has little impact on the entire battery module, after multiple cycles, overcharged and over-discharged cells may develop internal structural changes such as micro-short circuits, significantly affecting the entire battery module. In severe cases, this can lead to battery combustion and explosion, threatening personal safety. Therefore, accurate detection of overcharging and over-discharging of individual cells is of paramount importance for the research, development, production, and maintenance of electric vehicles, as well as ensuring the safety of drivers and passengers.

[0003] Currently, commonly used methods for detecting overcharge and over-discharge of lithium-ion batteries mainly involve chemical measurement methods such as scanning electron microscopy and X-ray diffraction to detect the battery's electrochemical performance and internal structural morphology. These methods cannot obtain the battery's state in a timely manner, are destructive to the battery, and have a narrow detection frequency domain, failing to fully obtain information on the battery's kinetics and electrode interface structure. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the purpose of this disclosure is to provide a method for detecting overcharge and over-discharge of lithium batteries based on electrochemical impedance spectroscopy. This method can effectively detect the overcharge and over-discharge states of batteries without damaging the battery structure.

[0005] To achieve the above objectives, this disclosure provides the following technical solutions:

[0006] A method for detecting overcharge and over-discharge of lithium batteries based on electrochemical impedance spectroscopy includes the following steps:

[0007] S100: Constructing the equivalent circuit model of a lithium battery;

[0008] S200: Measure the electrochemical impedance spectroscopy of a new lithium battery under standard charge and discharge conditions;

[0009] S300: Based on the electrochemical impedance spectrum of the new lithium battery under standard charge and discharge conditions, the parameters of each device in the equivalent circuit model are identified to obtain the diffusion index and equivalent capacitance of the new lithium battery under standard charge and discharge conditions.

[0010] S400: Measure the electrochemical impedance spectroscopy of the lithium battery under test after a certain number of charge-discharge cycles;

[0011] S500: Based on the electrochemical impedance spectrum of the lithium battery under test, the parameters of each device in the equivalent circuit model are identified to obtain the diffusion index and equivalent capacitance of the lithium battery under test after a certain number of charge-discharge cycles.

[0012] S600: The diffusion index of the lithium battery under test after a certain number of charge-discharge cycles is compared with the diffusion index of a new lithium battery under standard charge-discharge conditions to determine whether the lithium battery under test is in an over-discharge state.

[0013] S700: The equivalent capacitance of the lithium battery under test after a certain number of charge-discharge cycles is compared with the equivalent capacitance of a new lithium battery under standard charge-discharge conditions to determine whether the lithium battery under test is in an overcharged state.

[0014] Preferably, the equivalent circuit model of the lithium battery includes: an inductor L, inductor L connected in series with a first resistor R0, a first constant phase angle element CPE1 and a second constant phase angle element CPE2, the first constant phase angle element CPE1 connected in parallel with a second resistor R1, the second constant phase angle element CPE2 connected in parallel with a second resistor R2, and the second resistor R2 connected in series with an impedance Zw.

[0015] Preferably, in step S600, if the diffusion index of the lithium battery under test after a certain number of charge-discharge cycles is less than the diffusion index of the new lithium battery under standard charge-discharge, then the lithium battery under test is in an over-discharge state; if it is greater, then step S700 is executed.

[0016] Preferably, in step S700, if the equivalent capacitance of the lithium battery under test after a certain number of charge-discharge cycles is less than the equivalent capacitance of a new lithium battery under standard charge-discharge conditions, then the lithium battery under test is in an overcharged state; if it is greater, then it is in a normal state.

[0017] Preferably, the detection temperature for the lithium battery is 25°C.

[0018] This disclosure also proposes a lithium battery overcharge and over-discharge detection device based on electrochemical impedance spectroscopy, comprising:

[0019] Model building unit, used to build the equivalent circuit model of a lithium battery;

[0020] The first measurement unit is used to measure the electrochemical impedance spectroscopy of the new lithium battery.

[0021] The first identification unit is used to identify the parameters of each device in the equivalent circuit model based on the electrochemical impedance spectrum of the new lithium battery under standard charge and discharge conditions, so as to obtain the diffusion index and equivalent capacitance of the new lithium battery under standard charge and discharge conditions.

[0022] The second measurement unit is used to measure the electrochemical impedance spectroscopy of the lithium battery under test after a certain number of charge-discharge cycles.

[0023] The second identification unit is used to identify the parameters of each device in the equivalent circuit model based on the electrochemical impedance spectrum of the lithium battery under test, so as to obtain the diffusion index and equivalent capacitance of the lithium battery under test after a certain number of charge and discharge cycles.

[0024] The first judgment unit is used to compare the diffusion index of the lithium battery under test after a certain number of charge-discharge cycles with the diffusion index of a new lithium battery under standard charge-discharge conditions in order to determine whether the lithium battery under test is in an over-discharge state.

[0025] The second judgment unit is used to compare the equivalent capacitance of the lithium battery under test after a certain number of charge-discharge cycles with the equivalent capacitance of a new lithium battery under standard charge-discharge conditions in order to determine whether the lithium battery under test is in an overcharged state.

[0026] Compared with the prior art, the beneficial effects of this disclosure are as follows:

[0027] The method described in this disclosure can obtain the state of lithium batteries in a timely manner without damaging the batteries. The batteries can still be used after testing. It can also perform wide frequency domain testing, which can fully obtain the dynamics and electrode interface structure information of the batteries. It can detect batteries more specifically and comprehensively. Furthermore, this method does not need to know the current cycle number of the battery when detecting the overcharge and over-discharge state of the battery, which means it can detect batteries with unknown cycle numbers. Attached Figure Description

[0028] Figure 1 This is a flowchart of a lithium battery overcharge and over-discharge detection method based on electrochemical impedance spectroscopy provided in one embodiment of this disclosure;

[0029] Figure 2 This is a schematic diagram of the equivalent circuit model of a lithium battery provided in another embodiment of this disclosure;

[0030] Figure 3 This is a comparison of the equivalent circuit fitting curve and the experimentally obtained electrochemical impedance spectroscopy curve after 60 cycles of 2.0V over-discharge provided in another embodiment of this disclosure;

[0031] Figure 4 This is an error diagram of the equivalent circuit fitting curve and the experimentally obtained electrochemical impedance spectroscopy curve after 60 cycles of 2.0V over-discharge provided in another embodiment of this disclosure;

[0032] Figure 5 This is an error diagram of the equivalent circuit fitting curve and the experimentally obtained electrochemical impedance spectroscopy curve during 60 cycles of overcharging at 4.3V provided in another embodiment of this disclosure;

[0033] Figure 6 This is an error diagram of the equivalent circuit fitting curve and the experimentally obtained electrochemical impedance spectroscopy curve when 2.4V over-discharged for 50 cycles, provided in another embodiment of this disclosure. Detailed Implementation

[0034] The following will refer to the appendix. Figures 1 to 6 Specific embodiments of this disclosure are described in detail. While specific embodiments of this disclosure are shown in the accompanying drawings, it should be understood that this disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of this disclosure to those skilled in the art.

[0035] It should be noted that certain terms are used in the specification and claims to refer to specific components. Those skilled in the art will understand that different terms may be used to refer to the same component. This specification and claims do not distinguish components based on differences in terminology, but rather on differences in function. The terms "comprising" or "including" used throughout the specification and claims are open-ended and should be interpreted as "comprising but not limited to." The following descriptions are preferred embodiments for carrying out this disclosure; however, these descriptions are for the purpose of understanding the general principles of the specification and are not intended to limit the scope of this disclosure. The scope of protection of this disclosure is determined by the appended claims.

[0036] To facilitate understanding of the embodiments of this disclosure, further explanations and descriptions will be provided below with reference to the accompanying drawings and specific embodiments. The accompanying drawings do not constitute a limitation on the embodiments of this disclosure.

[0037] In one embodiment, such as Figure 1 As shown, this disclosure proposes a method for detecting overcharge and over-discharge of lithium batteries based on electrochemical impedance spectroscopy, comprising the following steps:

[0038] S100: Constructing the equivalent circuit model of a lithium battery;

[0039] S200: Measure the electrochemical impedance spectroscopy of a new lithium battery under standard charge and discharge conditions;

[0040] S300: Based on the electrochemical impedance spectrum of the new lithium battery under standard charge and discharge conditions, the parameters of each device in the equivalent circuit model are identified to obtain the diffusion index and equivalent capacitance of the new lithium battery under standard charge and discharge conditions.

[0041] S400: Measure the electrochemical impedance spectroscopy of the lithium battery under test after a certain number of charge-discharge cycles;

[0042] S500: Based on the electrochemical impedance spectrum of the lithium battery under test, the parameters of each device in the equivalent circuit model are identified to obtain the diffusion index and equivalent capacitance of the lithium battery under test after a certain number of charge-discharge cycles.

[0043] S600: The diffusion index of the lithium battery under test after a certain number of charge-discharge cycles is compared with the diffusion index of a new lithium battery under standard charge-discharge conditions to determine whether the lithium battery under test is in an over-discharge state.

[0044] S700: The equivalent capacitance of the lithium battery under test after a certain number of charge-discharge cycles is compared with the equivalent capacitance of a new lithium battery under standard charge-discharge conditions to determine whether the lithium battery under test is in an overcharged state.

[0045] The above embodiments constitute the complete technical solution of this disclosure. This embodiment can obtain the state of the lithium battery in a timely manner without damaging the battery. The battery can still be used after testing. It can also perform wide-frequency domain testing, which can fully obtain the dynamics and electrode interface structure information of the battery. This allows for more specific and comprehensive testing of the battery. Furthermore, this embodiment does not need to know the current cycle number of the battery when detecting overcharge and over-discharge states, thus enabling testing of batteries with unknown cycle numbers and improving testing efficiency.

[0046] In another embodiment, such as Figure 2 As shown, the equivalent circuit model of the lithium battery includes: an inductor L, inductor L connected in series with a first resistor R0, a first constant phase angle element CPE1 and a second constant phase angle element CPE2, the first constant phase angle element CPE1 connected in parallel with a second resistor R1, the second constant phase angle element CPE2 connected in parallel with a second resistor R2, and the second resistor R2 connected in series with an impedance Zw.

[0047] In this embodiment, the components in the equivalent circuit model are explained as follows:

[0048] (1) Inductor element L

[0049] The inductor element L is used to characterize the contact inductance in the high-frequency region, which is the curve below the real axis in the electrochemical impedance spectroscopy; this part is a straight line almost perpendicular to the real axis. This part is caused by the contact inductance between the battery electrode and the measuring electrode. Since the position between the battery and the measuring electrode cannot be controlled during each measurement, it has a large degree of uncertainty. This paper uses an inductor L as an approximate equivalent for this part, but does not study this part in detail.

[0050] (2) Resistor element R0

[0051] The resistive element R0 is used to characterize the ohmic impedance of a lithium-ion battery, which is the intersection of the electrochemical impedance spectroscopy with the real axis. Through fitting simulation verification, the fitting result is close to the value of the intersection with the real axis. Therefore, the ohmic impedance value can be directly obtained from the electrochemical impedance spectroscopy curve without fitting simulation, simplifying the analysis of experimental results.

[0052] (3) Resistor R1 and constant phase angle element CPE1

[0053] A resistor R1 and a constant-phase-angle element CPE1 are connected in parallel to characterize the impedance of the solid electrolyte interphase (SEI) film formed at the solid-liquid interface due to the reaction between the lithium-ion battery anode material and the surrounding electrolyte solution. R1 represents the resistance of the SEI film, and CPE1 represents the capacitance of the SEI film due to the "diffusion effect." This parallel structure corresponds to the mid-to-high frequency region semicircle in the electrochemical impedance spectroscopy curve. The parameters of each element need to be obtained through fitting simulation.

[0054] (4) Resistor R2 and constant phase angle element CPE2

[0055] Resistive element R2 and constant phase angle element CPE2 are used to characterize the reaction impedance between the electrolyte solution and the positive and negative electrodes of a lithium-ion battery. R2 represents the charge transfer resistance of the interfacial reaction, and CPE2 represents the double-layer capacitance of the solid electrode due to the "diffusion effect." Similar to R1 and CPE1, this structure also forms a semicircle in the electrochemical impedance spectroscopy curve, corresponding to the mid-to-low frequency region. However, due to the influence of experimental temperature and the internal structure of the battery, the semicircle in the mid-to-high frequency region of the electrochemical impedance spectroscopy measured in this experiment coincides with the semicircle in the mid-to-low frequency region. To better reflect the internal structure of the battery, this paper uses two sets of R and CPE to represent one of the measured semicircles.

[0056] (5) Warburg impedance Zw

[0057] The Warburg impedance (Zw) is used to characterize the impedance formed by the diffusion of lithium ions within the solid active material of a lithium-ion battery due to concentration polarization. It corresponds to a straight line in the low-frequency region of the electrochemical impedance spectroscopy curve, with an angle of approximately 45° to the real axis.

[0058] Furthermore, this embodiment uses ZSimpWin electrochemical impedance spectroscopy fitting software to fit the electrochemical impedance spectroscopy curves using an equivalent circuit model to determine the parameters of each component. Table 1 shows the parameter fitting results of the lithium-ion battery after 60 over-discharge aging cycles at a lower cutoff voltage of 2.0V. Figure 3 The table shows a comparison between the cell curves obtained from the electrochemical impedance spectroscopy (EIS) instrument and the curves obtained through fitting software. Table 1 shows that the errors in the parameter values ​​of the equivalent circuit model are small and within acceptable limits. Figure 3 and Figure 4It can be clearly seen that the original electrochemical impedance spectroscopy curve and the fitted curve obtained through the equivalent circuit have a high degree of fit and matching, with small error and good fitting effect. This indicates that the equivalent circuit model conforms to the measured electrochemical impedance spectroscopy curve and can better represent the internal kinetic process of lithium-ion battery.

[0059] Table 1. Fitting results of equivalent circuit model parameters after 60 over-discharge aging cycles with a lower cutoff voltage of 2.0V.

[0060]

[0061]

[0062] Furthermore, the simulation results of various parameters of the lithium battery under equivalent circuit models at 4.35V overcharge cycle, standard cycle, and 2.0V overdischarge cycle are shown in Tables 4-2 to 4-9. The curves corresponding to each parameter are as follows: Figure 4 As shown.

[0063] Table 4-2 Fitting results for parameter R0

[0064]

[0065] Table 4-3 Fitting results for parameter CPE1-Y0

[0066]

[0067] Table 4-4 Fitting results for parameter CPE1-n

[0068]

[0069]

[0070] Table 4-5 R1 fitting results for parameters

[0071]

[0072] Table 4-6 Fitting results for parameter CPE2-Y0

[0073]

[0074] Table 4-7 Fitting results for parameter CPE2-n

[0075]

[0076] Table 4-8 R² Fitting Results

[0077]

[0078] Table 4-9 Fitting results for parameter W-Y0

[0079]

[0080] It should be noted that not all of the above parameters can be used to detect overcharge and over-discharge of lithium batteries. Some parameters have relatively large errors, while others show similar or almost no change due to overcharge and over-discharge cycles. Therefore, it is necessary to screen the parameters to determine the appropriate parameters for detecting battery overcharge and over-discharge.

[0081] Taking R0 as an example, under overcharge, over-discharge, and standard cycle conditions, R0 increases at different rates with the number of cycles. However, during battery testing, we do not know the number of cycles. The same R0 may represent a situation with fewer cycles under overcharge conditions or a situation with more cycles under standard charge and discharge conditions. Therefore, the state of the battery cannot be determined based on the R0 value. Based on the changes in the parameters, the diffusion index CPE1-n and the equivalent capacitance CPE2-Y0 are ultimately selected as the detection parameters for battery overcharge and over-discharge.

[0082] In another embodiment, in step S600, if the diffusion index CPE1-n of the lithium battery under test after a certain number of charge-discharge cycles is less than the diffusion index CPE1-n of the new lithium battery under standard charge-discharge, then the lithium battery under test is in an over-discharge state; if it is greater, then step S700 is executed.

[0083] In this embodiment, under over-discharge cycling, CPE1-n decreases continuously with the number of cycles, while under overcharge and standard cycling, CPE1-n increases continuously with the number of cycles. Therefore, the value of CPE1-n can be used to distinguish whether the lithium battery is in an over-discharge state. Let the CPE1-n of a new lithium battery under standard discharge be x. Then, if the CPE1-n of the lithium battery under test is less than x after a certain number of charge-discharge cycles, the lithium battery is determined to be in an over-discharge state; otherwise, the battery is in an overcharged or normal state.

[0084] In another embodiment, in step S700, if the equivalent capacitance CPE2-Y0 of the lithium battery under test after a certain number of charge-discharge cycles is less than the equivalent capacitance CPE2-Y0 of the new lithium battery under standard charge-discharge conditions, then the lithium battery under test is in an overcharged state; if it is greater, then it is in a normal state.

[0085] In this embodiment, it is also necessary to further determine whether the lithium battery is in an overcharged or normal state. Under overcharge cycles, CPE2-Y0 decreases continuously with the number of cycles, while under over-discharge and standard cycles, CPE2-Y0 gradually increases with the number of cycles. Therefore, the CPE2-Y0 data can be used to determine whether the lithium battery is in an overcharged state. Let y be the CPE2-Y0 of a new lithium battery under standard charging. When the CPE2-Y0 of the tested lithium battery is less than y after a certain number of charge-discharge cycles, the lithium battery is in an overcharged state; otherwise, the battery is in a normal state.

[0086] The method described in this disclosure will now be verified with reference to specific embodiments.

[0087] (1) Overcharge detection

[0088] First, two new NCR18650GA lithium batteries were selected for electrochemical impedance spectroscopy (EIS) analysis, yielding CPE1-n = 0.5496 and CPE2-Y0 = 0.3453. Then, the new lithium batteries were overcharged at 4.3V and cycled 60 times. EIS analysis was performed on the overcharge-cycled lithium batteries, and simulation fitting yielded the following parameters in the model after 60 overcharge cycles: CPE1-n = 0.589 and CPE2-Y0 = 0.3317. Figure 5 The error plot between the equivalent circuit fitting curve and the electrochemical impedance spectroscopy curve is shown below. Figure 5 As can be seen, the curve fitting error is small, indicating that the lithium battery is in an overcharge cycle state, which is consistent with the actual situation.

[0089] (2) Over-discharge detection

[0090] First, the initial values ​​of the new lithium battery, CPE1-n = 0.5481 and CPE2-Y0 = 0.3460, were obtained through the same operation. Then, the new lithium battery was over-discharged at 2.4V and cycled 50 times. Electrochemical impedance spectroscopy was then performed on the over-discharged battery, and simulation fitting was used to obtain the parameters CPE1-n = 0.4406 and CPE2-Y0 = 0.4243 in the model after 50 over-discharge cycles. Figure 6 The error plot between the equivalent circuit fitting curve and the electrochemical impedance spectroscopy curve is shown below. Figure 6 As can be seen, the curve fitting error is small, indicating that the battery is in an over-discharge cycle state, which is consistent with the actual situation.

[0091] In another embodiment, this disclosure also proposes a lithium battery overcharge and over-discharge detection device based on electrochemical impedance spectroscopy, comprising:

[0092] Model building unit, used to build the equivalent circuit model of a lithium battery;

[0093] The first measurement unit is used to measure the electrochemical impedance spectroscopy of the new lithium battery.

[0094] The first identification unit is used to identify the parameters of each device in the equivalent circuit model based on the electrochemical impedance spectrum of the new lithium battery under standard charge and discharge conditions, so as to obtain the diffusion index and equivalent capacitance of the new lithium battery under standard charge and discharge conditions.

[0095] The second measurement unit is used to measure the electrochemical impedance spectroscopy of the lithium battery under test after a certain number of charge-discharge cycles.

[0096] The second identification unit is used to identify the parameters of each device in the equivalent circuit model based on the electrochemical impedance spectrum of the lithium battery under test, so as to obtain the diffusion index and equivalent capacitance of the lithium battery under test after a certain number of charge and discharge cycles.

[0097] The first judgment unit is used to compare the diffusion index of the lithium battery under test after a certain number of charge-discharge cycles with the diffusion index of a new lithium battery under standard charge-discharge conditions in order to determine whether the lithium battery under test is in an over-discharge state.

[0098] The second judgment unit is used to compare the equivalent capacitance of the lithium battery under test after a certain number of charge-discharge cycles with the equivalent capacitance of a new lithium battery under standard charge-discharge conditions in order to determine whether the lithium battery under test is in an overcharged state.

[0099] The foregoing general description of the invention and its specific embodiments should not be construed as a limitation on the technical solution of the invention. Those skilled in the art, based on the disclosure of this application, can add, reduce, or combine the disclosed technical features in the foregoing general description and / or specific embodiments (including examples) without departing from the constituent elements of the invention, to form other technical solutions within the scope of protection of this application.

Claims

1. A method for detecting overcharge and over-discharge of lithium batteries based on electrochemical impedance spectroscopy, comprising the following steps: S100: Constructing the equivalent circuit model of a lithium battery; S200: Measure the electrochemical impedance spectroscopy of a new lithium battery under standard charge and discharge conditions; S300: Based on the electrochemical impedance spectrum of the new lithium battery under standard charge and discharge conditions, the parameters of each device in the equivalent circuit model are identified to obtain the diffusion index and equivalent capacitance of the new lithium battery under standard charge and discharge conditions. S400: Measure the electrochemical impedance spectroscopy of the lithium battery under test after a certain number of charge-discharge cycles; S500: Based on the electrochemical impedance spectrum of the lithium battery under test, the parameters of each device in the equivalent circuit model are identified to obtain the diffusion index and equivalent capacitance of the lithium battery under test after a certain number of charge-discharge cycles. S600: The diffusion index of the lithium battery under test after a certain number of charge-discharge cycles is compared with the diffusion index of a new lithium battery under standard charge-discharge conditions to determine whether the lithium battery under test is in an over-discharge state. S700: Compare the equivalent capacitance of the lithium battery under test after a certain number of charge-discharge cycles with the equivalent capacitance of a new lithium battery under standard charge-discharge conditions to determine whether the lithium battery under test is in an overcharged state. in, The equivalent circuit model of the lithium battery includes: an inductor L, inductor L connected in series with a first resistor R0, a first constant phase angle element CPE1 and a second constant phase angle element CPE2, the first constant phase angle element CPE1 connected in parallel with a second resistor R1, the second constant phase angle element CPE2 connected in parallel with a second resistor R2, and the second resistor R2 connected in series with an impedance Zw.

2. The method according to claim 1, wherein, In step S600, if the diffusion index of the lithium battery under test after a certain number of charge-discharge cycles is less than the diffusion index of the new lithium battery under standard charge-discharge conditions, then the lithium battery under test is in an over-discharge state; if it is greater, then step S700 is executed.

3. The method according to claim 1, wherein, In step S700, if the equivalent capacitance of the lithium battery under test after a certain number of charge-discharge cycles is less than the equivalent capacitance of a new lithium battery under standard charge-discharge conditions, then the lithium battery under test is in an overcharged state; if it is greater, then it is in a normal state.

4. The method according to claim 1, wherein, The testing temperature for lithium batteries is 25℃.

5. A lithium battery overcharge and over-discharge detection device based on electrochemical impedance spectroscopy, comprising: Model building unit, used to build the equivalent circuit model of a lithium battery; The first measurement unit is used to measure the electrochemical impedance spectroscopy of the new lithium battery. The first identification unit is used to identify the parameters of each device in the equivalent circuit model based on the electrochemical impedance spectrum of the new lithium battery under standard charge and discharge conditions, so as to obtain the diffusion index and equivalent capacitance of the new lithium battery under standard charge and discharge conditions. The second measurement unit is used to measure the electrochemical impedance spectroscopy of the lithium battery under test after a certain number of charge-discharge cycles. The second identification unit is used to identify the parameters of each device in the equivalent circuit model based on the electrochemical impedance spectrum of the lithium battery under test, so as to obtain the diffusion index and equivalent capacitance of the lithium battery under test after a certain number of charge and discharge cycles. The first judgment unit is used to compare the diffusion index of the lithium battery under test after a certain number of charge-discharge cycles with the diffusion index of a new lithium battery under standard charge-discharge conditions in order to determine whether the lithium battery under test is in an over-discharge state. The second judgment unit is used to compare the equivalent capacitance of the lithium battery under test after a certain number of charge-discharge cycles with the equivalent capacitance of a new lithium battery under standard charge-discharge conditions in order to determine whether the lithium battery under test is in an overcharged state. The equivalent circuit model of the lithium battery includes: an inductor L, which is connected in series with a first resistor R0, a first constant phase angle element CPE1, and a second constant phase angle element CPE2. The first constant phase angle element CPE1 is connected in parallel with a second resistor R1, and the second constant phase angle element CPE2 is connected in parallel with a second resistor R2. The second resistor R2 is connected in series with an impedance Zw.

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