Impedance test method and application

Abstract

The invention provides an impedance test method and application, and the method comprises the steps: carrying out the constant volume test of a battery, and obtaining a first battery; adjusting the first battery to a preset SOC with a first constant current to obtain a second battery; standing the second battery, and recording the first voltage of the second battery after standing to obtain a third battery; performing pulse charging / discharging on the third battery with a second constant current, and recording a second voltage of the third battery after the pulse charging / discharging is started and a third voltage of the third battery when the pulse charging / discharging is finished; ohmic impedance of the third battery is obtained, and the total impedance value, electrochemical reaction impedance and diffusion impedance of the third battery are obtained according to the third voltage, the first voltage, the second voltage and the second constant current. According to the impedance testing method, the total impedance value and the impedance of each part of the battery can be calculated by testing the voltage of the battery after standing and the voltage of the battery after pulse charging or discharging, and the electrochemical process in the battery can be deeply analyzed.

Description

Technical Field

[0001] This application relates to the technical fields of impedance testing and secondary batteries, and particularly relates to a method for testing impedance and its application. Background Art

[0002] Battery impedance is one of the important parameters of battery performance. It directly affects the charge and discharge efficiency, power output ability, and cycle life of the battery. The main testing methods include electrochemical impedance spectroscopy (EIS) method, single-frequency (1000 Hz) alternating current impedance (ACR) testing, pulsed direct current impedance (DCR) testing, etc.

[0003] The ACR measured by the alternating current impedance method (usually at a frequency of 1000 Hz) can evaluate the ohmic impedance (Rs) of the battery. The EIS method is more comprehensive and can be used to decompose the impedance of each part of the battery. However, when testing the impedance of the positive and negative electrodes separately by the EIS method, the battery needs to be disassembled, and the positive or negative electrode is assembled into a positive / positive symmetric battery or a negative / negative symmetric battery for testing, which is a destructive testing method. And the non-destructive EIS testing based on the three-electrode system has high requirements for the production of the three electrodes (such as the integrity of lithium in the lithium-plated electrode will affect the test results). Moreover, the related impedance of the reference electrode will still be introduced, and the results are not accurate. In addition, the EIS method needs to fit the impedance spectrum to obtain the impedance of each part of the battery. Therefore, it has a great dependence on the fitting model and the selection of the fitting region, which is likely to cause inaccurate test results.

[0004] The DCR test is close to the actual working conditions, the test method is simple, and it can directly and accurately evaluate the battery performance and health status, and the test reproducibility is good. However, the traditional DCR test usually can only obtain the overall impedance value of the battery, cannot split the overall impedance of the battery, and at the same time cannot distinguish the impedance contributions of the positive and negative electrodes respectively. Summary of the Invention

[0005] In order to solve the problems in the prior art that the test results of battery impedance testing are inaccurate, the test process is complex, the battery is damaged, the overall impedance of the battery cannot be split, and at the same time the impedance contributions of the positive and negative electrodes cannot be distinguished, an object of this application is to provide a method for testing impedance. By testing the voltage of the battery after standing, the voltage and ohmic impedance at a preset time after pulsed charging or discharging, and the total impedance value and each part of the impedance (electrochemical reaction impedance and diffusion impedance) of the battery can be calculated according to them, which is beneficial to deeply analyze the internal electrochemical process of the battery and is of great significance for battery optimization and battery failure analysis.

[0006] Another object of this application relates to the application of the method for testing impedance in the field of secondary batteries.

[0007] To achieve the above object, a first aspect of the present application provides a method for testing impedance, including:

[0008] Performing a constant volume test on a battery to obtain a first battery;

[0009] Adjusting the first battery to a preset SOC at a first constant current to obtain a second battery;

[0010] Letting the second battery stand still and recording a first voltage of the second battery after standing still to obtain a third battery;

[0011] Performing pulsed charging or pulsed discharging on the third battery at a second constant current, and recording a second voltage of the third battery after the start of the pulsed charging or pulsed discharging and a third voltage of the third battery at the end;

[0012] Obtaining the ohmic impedance of the third battery, taking the absolute value of the ratio of the difference between the third voltage and the first voltage to the second constant current as the total impedance value of the third battery, taking the absolute value of the ratio of the difference between the second voltage and the first voltage to the second constant current as the impedance sum of the third battery, the impedance sum of the third battery being the sum of the ohmic impedance of the third battery and the electrochemical reaction impedance of the third battery, taking the difference between the total impedance value of the third battery and the impedance sum of the third battery as the diffusion impedance of the third battery, and taking the difference between the impedance sum of the third battery and the ohmic impedance of the third battery as the electrochemical reaction impedance of the third battery.

[0013] In some embodiments, the battery is a three - electrode battery, and the three - electrode battery includes a secondary battery; and / or, the reference electrode of the three - electrode battery includes one of a lithium electrode, a lithium - plated electrode, a sodium electrode, and a sodium - plated electrode; and / or, during the testing process of the method for testing battery impedance, the battery is placed in a battery test cabinet, and the voltages between the positive electrode and the reference electrode and between the negative electrode and the reference electrode are recorded through a multi - channel recorder.

[0014] In some embodiments, the method for testing battery impedance further includes:

[0015] Recording a fourth voltage of the positive electrode after standing still;

[0016] Recording a fifth voltage of the positive electrode after the start of the pulsed charging or pulsed discharging and a sixth voltage of the positive electrode at the end;

[0017] Taking the absolute value of the ratio of the difference between the sixth voltage and the fourth voltage to the second constant current as the total impedance value of the positive electrode, taking the absolute value of the ratio of the difference between the fifth voltage and the fourth voltage to the second constant current as the impedance sum of the positive electrode, the impedance sum of the positive electrode being the sum of the ohmic impedance of the positive electrode and the electrochemical reaction impedance of the positive electrode, and taking the difference between the total impedance value of the positive electrode and the impedance sum of the positive electrode as the diffusion impedance of the positive electrode.

[0018] In some embodiments, the method for testing the battery impedance further includes:

[0019] Recording the seventh voltage of the negative electrode after the standing;

[0020] Recording the eighth voltage of the negative electrode after the start of the pulsed charging or pulsed discharging and the ninth voltage of the negative electrode at the end;

[0021] Taking the absolute value of the ratio of the difference between the ninth voltage and the seventh voltage to the second constant current as the total impedance value of the negative electrode, taking the absolute value of the ratio of the absolute value of the difference between the eighth voltage and the seventh voltage to the second constant current as the impedance sum of the negative electrode, the impedance sum of the negative electrode being the sum of the ohmic impedance of the negative electrode and the electrochemical reaction impedance of the negative electrode, and taking the difference between the total impedance value of the negative electrode and the impedance sum of the negative electrode as the diffusion impedance of the negative electrode.

[0022] The second aspect of the present application also relates to the application of the method for testing the impedance described in the present application in the field of secondary batteries.

[0023] The method for testing the impedance described in the present application can at least bring the following beneficial effects:

[0024] 1. By testing the voltage after the battery stands, the voltage and ohmic impedance at a preset time after pulsed charging or discharging, and calculating the total impedance value of the battery (the third battery) and each part of the impedance (electrochemical reaction impedance and diffusion impedance) based on them, it is beneficial to deeply analyze the internal electrochemical process of the battery, which is of great significance for battery optimization and battery failure analysis.

[0025] 2. With the help of the three-electrode system, the potentials and impedances of the positive and negative electrodes can be measured separately, and they can be further decomposed in a similar way to the battery impedance to obtain the sum of the ohmic impedance and the electrochemical reaction impedance of the positive and negative electrodes respectively, and the diffusion impedance, which can distinguish the impedance contributions of the positive and negative electrodes, is beneficial to further deeply analyze the internal electrochemical process of the battery, and is of great significance for battery optimization and battery failure analysis.

[0026] 3. When using a three - electrode system, the method for measuring this impedance is a non - destructive analysis method, with lower requirements for fabricating the three electrodes compared to the EIS method, and it is closer to the actual working conditions. The test method is simple, can directly and accurately evaluate the battery performance and health status, and has good test reproducibility.

[0027] Additional aspects and advantages of the present application will be given in part in the following description, become apparent in part from the following description, or be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The above - mentioned and / or additional aspects and advantages of the present application will become apparent and be easily understood from the following description of the embodiments in conjunction with the drawings.

[0029] Wherein:

[0030] Figure 1 is a flowchart of the method for measuring the impedance shown in an exemplary embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] Embodiments of the present application will be described in detail below. Examples of the embodiments are shown in the drawings. The embodiments described below with reference to the drawings are exemplary and are intended to explain the present application, and should not be construed as a limitation to the present application.

[0032] In the present application, the disclosure of a numerical range includes all values within the entire range and the disclosure of further sub - ranges, including the endpoints and sub - ranges given for these ranges.

[0033] In the present application, for the raw materials, equipment, etc. involved, unless otherwise specified, they are raw materials and equipment that can be obtained through commercial channels or made by known methods; for the methods involved, unless otherwise specified, they are conventional methods.

[0034] The term “and / or” when used in a list containing two or more items means that any one of the listed items can be used alone or in combination with any one or more of the listed items. For example, the expression “A and / or B” is intended to mean A or B or A and B, that is, it means only A, only B, or the combination of A and B.

[0035] The inventors found that traditional DCR tests usually only obtain the impedance value of the overall battery and cannot distinguish the impedance contributions of the positive and negative electrodes. The three-electrode system can measure the potential and impedance of the positive and negative electrodes separately. It is a non-destructive testing method and can further obtain the impedance of each part of the battery (ohmic impedance, electrochemical reaction impedance, and diffusion impedance) through decomposition, which is of great significance for battery optimization and battery failure analysis. In addition, the three-electrode DCR impedance testing method has lower requirements for the production of three electrodes compared to the three-electrode EIS method. The integrity of lithium plating / sodium plating on the three electrodes has less impact on the test, so the operation is simpler and the test results have good reproducibility. Therefore, this application aims to test the DCR impedance of the full battery, positive electrode, and negative electrode, including decomposition impedance such as diffusion impedance, by means of the three-electrode system.

[0036] A method for testing impedance according to an embodiment of the present application will be described below with reference to the accompanying drawings.

[0037] Figure 1 It is a flowchart of a method for testing impedance shown in an exemplary embodiment of the present application.

[0038] As Figure 1 shown, the method for testing impedance includes the following steps:

[0039] S101. Perform a constant-volume test on the battery to obtain a first battery.

[0040] In the embodiments of the present application, there are no restrictions on the packaging form and battery system of the battery.

[0041] Exemplarily, in step S101, the packaging form of the battery includes but is not limited to soft pack, cylindrical, square, etc.

[0042] Exemplarily, in step S101, the battery system of the battery includes but is not limited to secondary batteries, such as lithium-ion batteries, sodium-ion batteries, etc.

[0043] As an optional example, in step S101, the battery is a three-electrode battery, and the three-electrode battery includes secondary batteries such as lithium-ion batteries and sodium-ion batteries.

[0044] In some embodiments, when the battery in step S101 is a three-electrode battery, the reference electrode of the three-electrode battery includes but is not limited to one of a lithium electrode, a lithium-plated electrode, a sodium electrode, a sodium-plated electrode, etc.

[0045] It should be noted that in the embodiments of the present application, the reference electrode used for the three-electrode battery needs to be selected according to the battery system. For example, a lithium electrode or a lithium-plated electrode is used for a lithium-ion battery, and a sodium electrode or a sodium-plated electrode is used for a sodium-ion battery.

[0046] In some embodiments, in step S101, the constant volume test of the battery includes: performing charge and discharge cycles on the battery.

[0047] In some embodiments, in the constant volume test, the rate used is 0.2C - 0.33C, including but not limited to 0.22C, 0.25C, 0.27C, or 0.3C, etc.

[0048] In some embodiments, in the constant volume test, the number of cycles is 2 - 3 times.

[0049] In some embodiments, in the constant volume test, the capacity of the last discharge cycle of the battery is used as the capacity of the battery after the constant volume test. For the convenience of description, the capacity of the battery after the constant volume test is denoted as C0.

[0050] In the embodiments of the present application, the specific structures and compositions of the positive electrode, negative electrode, etc. of the battery in step S101 are not limited and can be any positive electrode, negative electrode, etc. well-known in the art that can be used for secondary batteries, etc.

[0051] S102. Adjust the first battery obtained in step S101 to a preset SOC at a first constant current to obtain a second battery.

[0052] In some embodiments, the ratio of the first constant current to the capacity of the battery after the constant volume test is (0.2 - 1):1, that is, the first constant current is 0.2C0 to 1C0.

[0053] Exemplarily, the ratio of the first constant current to the capacity of the battery after the constant volume test includes but not limited to 0.3:1, 0.5:1, 0.7:1, or 0.9:1, etc.

[0054] In some embodiments, the method of adjusting the first battery to the preset SOC at the first constant current includes but not limited to charging, discharging, charging and discharging, etc.

[0055] In some embodiments, the preset SOC is 0 - 100% SOC, including but not limited to 20% SOC, 50% SOC, 80% SOC, 90% SOC, or 100% SOC, etc.

[0056] In the embodiments of the present application, the preset SOC can be adjusted according to the experimental requirements. When the preset SOC is 0, it represents an empty battery; when the preset SOC is 100%, it represents a full battery.

[0057] S103. Let the second battery obtained in step S102 stand and record the first voltage of the second battery after standing to obtain a third battery.

[0058] In some embodiments, the static placement includes a first static placement and a second static placement performed in sequence. In the embodiments of the present application, the second battery is subjected to the first static placement and the second static placement in sequence. The purpose of the first static placement is to ensure that the second battery reaches an equilibrium state. The purpose of the second static placement is as follows: after the first static placement, most of the polarization effects of the battery are basically eliminated. Through the second static placement, it can be determined whether the second battery reaches an equilibrium state (if the voltage change from the start to the end of the second static placement stage is less than 0.1 mV / min, it can be considered that the second battery reaches an equilibrium state. The second battery must meet this standard before subsequent tests can be carried out. Otherwise, the first static placement and the second static placement are repeated until the battery reaches an equilibrium state).

[0059] Therefore, the first voltage is the voltage of the second battery that reaches an equilibrium state after the static placement. The third battery is the second battery that reaches an equilibrium state.

[0060] In some embodiments, the method for testing impedance further includes a step of determining whether the second battery after the static placement reaches an equilibrium state before recording the first voltage of the second battery after the static placement.

[0061] As an optional example, determining whether the second battery after the static placement reaches an equilibrium state includes:

[0062] Obtaining the voltage change of the second battery from the start to the end of the second static placement stage;

[0063] If the voltage change of the second battery from the start to the end of the second static placement stage is less than 0.1 mV / min, it is determined that the second battery reaches an equilibrium state;

[0064] If the voltage change of the second battery from the start to the end of the second static placement stage is above 0.1 mV / min, it is determined that the second battery does not reach an equilibrium state.

[0065] Exemplarily, the method for obtaining the voltage change of the second battery from the start to the end of the second static placement stage is to monitor in real time (for example, test once every 0.05 - 0.5 s) and record the voltage of the second battery during the second static placement stage.

[0066] In some embodiments, the method for testing impedance further includes:

[0067] When the determination result is that the second battery does not reach an equilibrium state, repeat the steps of the static placement (the first static placement and the second static placement) until it is determined that the second battery reaches an equilibrium state (the voltage change from the start to the end of the second static placement stage is less than 0.1 mV / min).

[0068] In some embodiments, the time of the first static placement is 0.5 - 1.5 h, including but not limited to 0.75 h, 1 h, or 1.25 h, etc.

[0069] In some embodiments, the time of the second standing is from 30 s to 90 s, including but not limited to 45 s, 60 s, or 75 s, etc.

[0070] As an alternative example, the time of the first standing is 1 h, and the time of the second standing is 60 s.

[0071] In some embodiments, the voltage of the battery is recorded in real time during the standing process.

[0072] Exemplarily, the time interval for recording the voltage of the battery in real time during the standing process is 0.05 - 0.5 s, including but not limited to 0.05 s, 0.1 s, or 0.5 s, etc., and preferably 0.1 s.

[0073] In some embodiments, the first voltage is the voltage of the second battery at a first preset time at the end of the standing. Exemplarily, the first preset time is 0.05 - 0.5 s, including but not limited to 0.05 s, 0.1 s, or 0.5 s, etc.

[0074] As a preferred example, the first voltage is the voltage of the second battery at the last 0.1 s of the standing.

[0075] In some embodiments, when the battery in step S101 is a three - electrode battery, the three - electrode battery is placed in a battery test cabinet for DCR testing (i.e., the impedance testing of the present application), and the voltage of the positive electrode / reference electrode and the voltage of the negative electrode / reference electrode are measured through a multi - channel recorder.

[0076] It can be understood that the voltage of the positive electrode / reference electrode is the voltage of the positive electrode, and the voltage of the negative electrode / reference electrode is the voltage of the negative electrode.

[0077] In some embodiments, when the battery in step S101 is a three - electrode battery, the impedance testing method of the embodiment of the present application further includes the step of recording the voltage of the positive electrode and / or the voltage of the negative electrode in real time during the standing process.

[0078] Exemplarily, the time intervals for recording the voltage of the positive electrode and / or the voltage of the negative electrode in real time during the standing process are both 0.05 - 0.5 s, including but not limited to 0.05 s, 0.1 s, or 0.5 s, etc., and preferably 0.1 s.

[0079] In some embodiments, when the battery in step S101 is a three - electrode battery, the impedance testing method of the embodiment of the present application further includes the step of recording the fourth voltage of the positive electrode after the standing.

[0080] In some embodiments, the fourth voltage is the voltage of the positive electrode at the last fourth preset time of the standing still. Exemplarily, the fourth preset time is 0.05 - 0.5 s, including but not limited to 0.05 s, 0.1 s, or 0.5 s, etc.

[0081] As a preferred example, the fourth voltage is the voltage of the positive electrode at the last 0.1 s of the standing still.

[0082] In some embodiments, when the battery in step S101 is a three - electrode battery, the impedance testing method of the embodiment of the present application further includes the step of recording the seventh voltage of the negative electrode after the standing still.

[0083] In some embodiments, the seventh voltage is the voltage of the positive electrode at the last seventh preset time of the standing still. Exemplarily, the seventh preset time is 0.05 - 0.5 s, including but not limited to 0.05 s, 0.1 s, or 0.5 s, etc.

[0084] As a preferred example, the seventh voltage is the voltage of the negative electrode at the last 0.1 s of the standing still.

[0085] S104. Pulse - charge or pulse - discharge the third battery obtained in step S103 with a second constant current, and record the second voltage of the third battery after the start of the pulse - charge or pulse - discharge and the third voltage of the third battery at the end.

[0086] In some embodiments, the ratio of the second constant current to the capacity of the battery after the constant - volume test is (0.2 - 5):1, that is, the second constant current is 0.2C0 to 5C0. In the embodiments of the present application, when the ratio of the second constant current to the capacity of the battery after the constant - volume test is within the above range, it is convenient to simulate the polarization situation of the battery under actual working conditions and test the impedance value of the battery under actual working conditions (currently, the charge - discharge rate in the industry is generally within 5C); if it is lower than 0.2:1, it may lead to a decrease in the current detection accuracy and inaccurate test results. Exemplarily, the ratio of the second constant current to the capacity of the battery after the constant - volume test includes but not limited to 0.5:1, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, or 4.5:1, etc., and can be selected as (2 - 3):1.

[0087] Since the battery is prone to lithium precipitation at low temperatures (such as below 0 °C), and the rate is generally below 1C at low temperatures, therefore, in the embodiments of the present application, when the test is carried out under low - temperature conditions, the second constant current is below 1C.

[0088] In some embodiments, the time of the pulse - charge or pulse - discharge is 10 - 60 s, including but not limited to 20 s, 30 s, 40 s, or 50 s, etc., and can be selected as 10 s.

[0089] In some embodiments, the method for testing the impedance further includes: during the process of pulse charging or discharging, the voltage of the third battery is recorded in real time.

[0090] Exemplarily, the time interval for recording the voltage of the third battery in real time during the process of pulse charging or discharging is 0.05 - 0.5 s, including but not limited to 0.05 s, 0.1 s, or 0.5 s, etc., and preferably 0.1 s.

[0091] In some embodiments, the second voltage is the voltage of the third battery at the initial second preset time during the pulse charging or pulse discharging. Exemplarily, the second preset time is 0.05 - 0.5 s, including but not limited to 0.05 s, 0.1 s, or 0.5 s, etc.

[0092] As a preferred example, the second voltage is the voltage of the third battery at the initial 0.1 s (i.e., the first 0.1 s) during the pulse charging or pulse discharging.

[0093] In some embodiments, the third voltage is the voltage of the third battery at the last third preset time during the pulse charging or pulse discharging. Exemplarily, the third preset time is 0.05 - 0.5 s, including but not limited to 0.05 s, 0.1 s, or 0.5 s, etc.

[0094] As a preferred example, the third voltage is the voltage of the third battery at the last 0.1 s during the pulse charging or pulse discharging.

[0095] In some embodiments, when the battery in step S101 is a three - electrode battery, the method for testing the impedance further includes: during the process of pulse charging or discharging, the voltage of the positive electrode and the voltage of the negative electrode are recorded in real time.

[0096] Exemplarily, when the battery in step S101 is a three - electrode battery, the time intervals for recording the voltage of the positive electrode and the voltage of the negative electrode in real time during the process of pulse charging or discharging are both 0.05 - 0.5 s, including but not limited to 0.05 s, 0.1 s, or 0.5 s, etc., and preferably 0.1 s.

[0097] In some embodiments, when the battery in step S101 is a three - electrode battery, the method for testing the impedance in the embodiments of the present application further includes: recording the fifth voltage of the positive electrode after the start of the pulse charging or pulse discharging and the sixth voltage of the positive electrode at the end.

[0098] In some embodiments, the fifth voltage is the voltage of the positive electrode during the first fifth preset time of the pulse charging or pulse discharging. Exemplarily, the fifth preset time is 0.05 - 0.5 s, including but not limited to 0.05 s, 0.1 s, or 0.5 s, etc.

[0099] As a preferred example, the fifth voltage is the voltage of the positive electrode at the first 0.1 s (i.e., the first 0.1 s) of the pulse charging or pulse discharging.

[0100] In some embodiments, the sixth voltage is the voltage of the positive electrode during the last sixth preset time of the pulse charging or pulse discharging. Exemplarily, the sixth preset time is 0.05 - 0.5 s, including but not limited to 0.05 s, 0.1 s, or 0.5 s, etc.

[0101] As a preferred example, the sixth voltage is the voltage of the positive electrode at the last 0.1 s of the pulse charging or pulse discharging.

[0102] In some embodiments, when the battery in step S101 is a three - electrode battery, the impedance testing method of the embodiments of the present application further includes: recording the eighth voltage of the negative electrode after the start of the pulse charging or pulse discharging and the ninth voltage of the negative electrode at the end.

[0103] In some embodiments, the eighth voltage is the voltage of the negative electrode during the first eighth preset time of the pulse charging or pulse discharging. Exemplarily, the eighth preset time is 0.05 - 0.5 s, including but not limited to 0.05 s, 0.1 s, or 0.5 s, etc.

[0104] As a preferred example, the eighth voltage is the voltage of the negative electrode at the first 0.1 s (i.e., the first 0.1 s) of the pulse charging or pulse discharging.

[0105] In some embodiments, the ninth voltage is the voltage of the negative electrode during the last ninth preset time of the pulse charging or pulse discharging. Exemplarily, the ninth preset time is 0.05 - 0.5 s, including but not limited to 0.05 s, 0.1 s, or 0.5 s, etc.

[0106] As a preferred example, the ninth voltage is the voltage of the negative electrode at the last 0.1 s of the pulse charging or pulse discharging.

[0107] S105. Obtain the ohmic impedance of the third battery described in step S103. Use the absolute value of the ratio of the difference between the third voltage and the first voltage to the second constant current as the total impedance value of the third battery, and use the absolute value of the ratio of the difference between the second voltage and the first voltage to the second constant current as the impedance sum of the third battery. The impedance sum of the third battery is the sum of the ohmic impedance of the third battery and the electrochemical reaction impedance of the third battery. Use the difference between the total impedance value of the third battery and the impedance sum of the third battery as the diffusion impedance of the third battery, and use the difference between the impedance sum of the third battery and the ohmic impedance of the third battery as the electrochemical reaction impedance of the third battery.

[0108] For the convenience of description, define the ohmic impedance of the third battery as R s , the third voltage as V3, the first voltage as V1, the second constant current as I, and the total impedance value of the third battery as R 总 , the second voltage as V2, and the electrochemical reaction impedance of the third battery as R 电 , and the diffusion impedance of the third battery as R 扩 , then the calculation formulas for various impedances of the third battery in step S105 can be expressed as:

[0109] The total impedance value R of the third battery 总 : R 总 = |(V3 - V1) / I|;

[0110] The impedance sum R of the third battery s + R 电 : R s + R 电 = |(V2 - V1) / I|;

[0111] The diffusion impedance R of the third battery 扩 : R 扩 = R 总 - (R s + R 电 );

[0112] The electrochemical reaction impedance R of the third battery 电 : R 电 = (R s + R 电 ) - R s .

[0113] In the embodiments of the present application, the battery is a full battery, and the electrochemical reaction impedance of the third battery can be understood as a further decomposition of the impedance of the full battery.

[0114] In some embodiments, the method for obtaining the ohmic impedance of the third battery in step S103 is: measured by an AC internal resistance meter (1000 Hz).

[0115] In some embodiments, when the battery in step S101 is a three-electrode battery, the impedance testing method of the embodiment of the present application further includes:

[0116] Taking the absolute value of the ratio of the difference between the sixth voltage and the fourth voltage to the second constant current as the total impedance value of the positive electrode, taking the absolute value of the ratio of the difference between the fifth voltage and the fourth voltage to the second constant current as the impedance sum of the positive electrode, the impedance sum of the positive electrode is the sum of the ohmic impedance of the positive electrode and the electrochemical reaction impedance of the positive electrode, and taking the difference between the total impedance value of the positive electrode and the impedance sum of the positive electrode as the diffusion impedance of the positive electrode.

[0117] For the convenience of expression, define the ohmic impedance of the positive electrode as R s ’, the sixth voltage as V6, the fourth voltage as V4, the second constant current as I as described above, and the total impedance value of the positive electrode as R 总 ’, the fifth voltage as V5, the electrochemical reaction impedance of the positive electrode as R 电 ’, and the diffusion impedance of the positive electrode as R 扩 ’, then the calculation formulas for various impedances of the positive electrode can be expressed as:

[0118] The total impedance value R 总 ’ of the positive electrode: R 总 ’ = |(V6 - V4) / I|;

[0119] The impedance sum R s ’ + R 电 ’ of the positive electrode: R s ’ + R 电 ’ = |(V5 - V4) / I|;

[0120] The diffusion impedance R 扩 ’ of the positive electrode: R 扩 ’ = R 总 ’ - (R s ’ + R 电 ’).

[0121] In some embodiments, when the battery in step S101 is a three-electrode battery, the impedance testing method of the embodiment of the present application further includes:

[0122] Taking the absolute value of the ratio of the difference between the ninth voltage and the seventh voltage to the second constant current as the total impedance value of the negative electrode, taking the absolute value of the ratio of the difference between the eighth voltage and the seventh voltage to the second constant current as the impedance sum of the negative electrode, the impedance sum of the negative electrode being the sum of the ohmic impedance of the negative electrode and the electrochemical reaction impedance of the negative electrode, and taking the difference between the total impedance value of the negative electrode and the impedance sum of the negative electrode as the diffusion impedance of the negative electrode.

[0123] For the convenience of expression, define the ohmic impedance of the negative electrode as R s ", the ninth voltage is V9, the seventh voltage is V7, the second constant current is I as described above, and the total impedance value of the negative electrode is R 总 ", the eighth voltage is V8, and the electrochemical reaction impedance of the negative electrode is R 电 ", the diffusion impedance of the negative electrode is R 扩 ", then the calculation formulas for various impedances of the negative electrode can be expressed as:

[0124] The total impedance value R of the negative electrode 总 ": R 总 " = |(V9 - V7) / I|;

[0125] The impedance sum R of the negative electrode s " + R 电 ": R s " + R 电 " = |(V8 - V7) / I|;

[0126] The diffusion impedance R of the negative electrode 扩 ": R 扩 " = R 总 " - (R s " + R 电 ").

[0127] It should be noted that in the embodiments of the present application, the "first", "second", "third", "fourth", "fifth", "sixth", "seventh", "eighth", and "ninth" related to voltage expressions are only for the convenience of distinction and are artificially named, without any substantial meaning, and only represent the voltages of the battery, the positive electrode, and the negative electrode in their respective specific states.

[0128] In some embodiments, the impedance testing method of the embodiments of the present application can be carried out in any temperature environment and can be used for any state of the battery (such as the early stage, middle stage, late stage, etc. of the cycle).

[0129] Exemplarily, the impedance testing method of the embodiments of the present application includes but is not limited to being carried out in temperature environments such as -30°C, -10°C, 10°C, 25°C, or 45°C.

[0130] In some embodiments, all impedances other than ohmic impedance involved in the impedance testing method of the embodiments of the present application are direct current resistances (DCR).

[0131] The impedance testing method of the embodiments of the present application can at least bring the following beneficial effects:

[0132] 1. By testing the voltage after the battery stands still, the voltage and ohmic impedance at a preset time after pulse charging or discharging, and calculating the total impedance value and each part impedance (electrochemical reaction impedance and diffusion impedance) of the battery (the third battery) based on them, it is beneficial to deeply analyze the internal electrochemical process of the battery, which is of great significance for battery optimization and battery failure analysis.

[0133] 2. With the help of a three - electrode system, the potentials and impedances of the positive and negative electrodes can be measured separately, and they can be further decomposed in a similar way to the battery impedance to obtain the sum of the ohmic impedance and electrochemical reaction impedance of each of the positive and negative electrodes, and the diffusion impedance, which can distinguish the impedance contributions of the positive and negative electrodes respectively, is beneficial to further deeply analyze the internal electrochemical process of the battery, and is of great significance for battery optimization and battery failure analysis.

[0134] 3. When using a three - electrode system, this impedance testing method is a non - destructive analysis method, with lower requirements for the production of the three - electrode compared to the EIS method, and it is closer to the actual working conditions. The testing method is simple, can directly and accurately evaluate the battery performance and health status, and has good test reproducibility.

[0135] The impedance testing method of the embodiments of the present application can be widely applied to secondary battery fields such as lithium - ion batteries and sodium - ion batteries.

[0136] Some features of the present technology are further illustrated in the following non - restrictive embodiments.

[0137] The lithium - ion batteries involved in the following examples and comparative examples are all lithium - iron - phosphate - graphite / silicon - based lithium - ion three - electrode soft - pack batteries, and the reference electrode is a lithium - plated electrode (lithium - plated copper wire). The preparation method of this lithium - iron - phosphate - graphite / silicon - based lithium - ion three - electrode battery includes the following steps:

[0138] (1) Preparation of the positive electrode: Lithium iron phosphate (Hunan Yuneng New Energy Y9E) as the positive electrode active material, conductive carbon black as the conductive agent, and polyvinylidene fluoride (PVDF) as the binder are mixed in a mass ratio of 97.1%: 1%: 1.9% with N - methylpyrrolidone (NMP) to obtain a positive electrode slurry; the positive electrode slurry is coated on the opposite two surface of a 13 - micron - thick aluminum foil positive electrode current collector, and after drying, rolling, and slitting, a positive electrode plate is obtained, with a positive electrode compaction density of 2.65 g / cm 3 , and the positive electrode areal density is 390 g / m2 。

[0139] (2) Preparation of the negative electrode: Mix graphite / silicon mixture (mass ratio of artificial graphite to vapor-deposited silicon carbide is 92%:8%) as the negative electrode active material, conductive carbon black and single-walled carbon nanotubes as conductive agents, carboxymethyl cellulose (CMC) as a binder, styrene-butadiene rubber (SBR) as a binder with deionized water in a mass ratio of 95.5%:1%:1.3%:2.2% to obtain a negative electrode slurry; coat the negative electrode slurry on the opposite two surfaces of a negative electrode current collector copper foil with a thickness of 5 microns, and after drying, rolling, and slitting, obtain a negative electrode sheet, and the negative electrode compaction density is 1.55 g / cm 3 , and the negative electrode areal density is designed according to an N / P ratio of 1.13 (the N / P ratio is the ratio of the negative electrode capacity to the positive electrode capacity under the same area).

[0140] (3) Obtaining the electrolyte: 1.1 M LiPF6, and the non-aqueous organic solvent is a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), ethyl methyl carbonate (EMC), and vinylene carbonate (VC), and the volume ratio is EC:DMC:FEC:EMC:VC = 30%:30%:10%:28%:2%.

[0141] (4) Selection of the separator: The polyethylene (PE) base film has a thickness of 9 microns, and the single-sided heat-resistant (ceramic) thickness is 3 microns.

[0142] (5) Assembly: Obtain a bare battery cell by laminating the above positive electrode sheet, negative electrode sheet, and separator. Insert a copper wire into the bare battery cell, and place a separator to separate the copper wire from the positive / negative electrodes to prevent short circuit; place the bare battery cell with the copper wire in an outer packaging shell, inject the electrolyte after drying, and through processes such as vacuum packaging, standing, formation, aging, grading, and lithium plating of the copper wire (reference electrode), obtain a lithium-ion three-electrode battery.

[0143] The sodium-ion batteries involved in the following examples and comparative examples are all sodium-ion three-electrode batteries with a sodium nickel iron manganese oxide and hard carbon system, which are square batteries, and the reference electrode is a sodium-plated electrode. The preparation method of the sodium-ion three-electrode battery with a sodium nickel iron manganese oxide and hard carbon system includes the following steps:

[0144] 1) Preparation of the positive electrode: Mix sodium nickel iron manganese oxide (NaNi 0.5 Fe 0.5 MnO4), conductive carbon black as a conductive agent, and PVDF as a binder with NMP in a mass ratio of 96%:2%:2% to obtain a positive electrode slurry; coat the positive electrode slurry on the opposite two surfaces of a positive electrode current collector aluminum foil with a thickness of 13 microns, and after drying, rolling, and slitting, obtain a positive electrode sheet, and the positive electrode compaction density is 3.2 g / cm3 , the positive electrode surface density is 350 g / m 2 .

[0145] 2) Preparation of the negative electrode: Hard carbon (Huamingsheng Co., Ltd. RHC-330) as the negative electrode active material, conductive carbon black as the conductive agent, CMC as the binder, and SBR as the binder are mixed with water in a mass ratio of 95.5%:1%:1.3%:2.2% to obtain a negative electrode slurry; the negative electrode slurry is coated on the opposite two side surfaces of a copper foil with a negative electrode current collector thickness of 6 microns, and after drying, rolling, and slitting, a negative electrode sheet is obtained, and the negative electrode compaction density is 0.9-1.0 g / cm 3 , and the negative electrode surface density is designed according to an N / P ratio of 1.2 (the N / P ratio is the ratio of the negative electrode capacity to the positive electrode capacity under the same area).

[0146] 3) Preparation of the electrolyte: 1 M / L NaPF6, and the non-aqueous organic solvent is a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), and ethyl methyl carbonate (EMC), and according to a volume ratio of EC:DMC:FEC:EMC = 30%:40%:5%:25%.

[0147] 4) Selection of the separator: A polyethylene (PE) base film is 9 microns, and the single-sided heat-resistant (ceramic) thickness is 3 microns.

[0148] 5) Assembly: The above positive electrode sheet, negative electrode sheet, and separator are wound to obtain a bare battery cell. A copper wire is inserted into the bare battery cell, and a separator is placed to separate the copper wire from the positive / negative electrodes to prevent short circuit; the bare battery cell with the copper wire is placed in an outer packaging shell, dried, and then the electrolyte is injected. After vacuum packaging, standing, formation, aging, grading, and sodium plating on the copper wire (reference electrode) and other processes, a sodium-ion three-electrode battery is obtained.

[0149] In the following examples, the tested three-electrode battery is placed in a battery test cabinet for DCR testing (the battery test cabinet tests the voltage of the battery), and the positive electrode / reference electrode voltage (i.e., the voltage of the positive electrode) and the negative electrode / reference electrode voltage (i.e., the voltage of the negative electrode) are recorded through a multi-channel recorder.

[0150] Example 1

[0151] The impedance testing method of this example includes the following steps:

[0152] S1. The battery is subjected to constant volume testing (charging-discharging cycle 3 times) at a current of 0.33C at room temperature (25°C), and the discharge capacity of the last cycle is taken as C0.

[0153] Among them, the battery is a lithium-ion battery, and C0 is 1.597 Ah.

[0154] S2. Charge the battery after the constant volume test in step S1 at a current of 1C0 for 30 min at room temperature (25°C) to adjust it to 50% SOC.

[0155] Among them, the 1C0 current is 1.597 A.

[0156] S3. Let the battery with 50% SOC obtained in step S2 stand still for 1 h at room temperature (25°C) to ensure that the battery reaches an equilibrium state. Subsequently, let it stand still for another 1 min at room temperature (25°C). During the first and second standing still processes, record the voltage of the battery, the voltage of the positive electrode, and the voltage of the negative electrode every 0.1 s. Record the voltage of the battery at the last 0.1 s during the second standing still process as V1, record the voltage of the positive electrode at the last 0.1 s during the second standing still process as V4, and record the voltage of the negative electrode at the last 0.1 s during the second standing still process as V7.

[0157] Among them, V1 = 3.3065 V, V4 = 3.422 V, V7 = 0.128 V.

[0158] S4. Perform a pulsed discharge on the battery that has been standing still twice in step S3 at a current of 2C0 for 10 s at room temperature (25°C). During the pulsed discharge process, record the voltage of the battery, the voltage of the positive electrode, and the voltage of the negative electrode every 0.1 s. Denote the current as I, denote the voltage of the battery at the first 0.1 s of the pulsed discharge as V2, denote the voltage of the battery at the last 0.1 s of the pulsed discharge as V3, denote the voltage of the positive electrode at the first 0.1 s of the pulsed discharge as V5, denote the voltage of the positive electrode at the last 0.1 s of the pulsed discharge as V6, denote the voltage of the negative electrode at the first 0.1 s of the pulsed discharge as V8, and denote the voltage of the negative electrode at the last 0.1 s of the pulsed discharge as V9.

[0159] Among them, I = 2C0 = 3.194 A, V2 = 3.2565 V, V3 = 3.2142 V, V5 = 3.404 V, V6 = 3.3805 V, V8 = 0.160 V, V9 = 0.178 V.

[0160] S5. Measure the ohmic impedance R of the battery (full battery) with an AC impedance meter (1000 Hz) s which is 5.3 mΩ, and calculate and decompose the impedance of the battery, the positive electrode, and the negative electrode respectively as follows:

[0161] Define the total impedance value of the battery as R 总 , the electrochemical reaction impedance of the battery as R 电 , the diffusion impedance of the battery as R 扩 , the ohmic impedance of the positive electrode as R s ’, the total impedance value of the positive electrode as R 总 ’, the electrochemical reaction impedance of the positive electrode as R 电 ’, the diffusion impedance of the positive electrode as R 扩', the ohmic impedance of the negative electrode is R s ", the total impedance value of the negative electrode is R 总 ", the electrochemical reaction impedance of the negative electrode is R 电 ", the diffusion impedance of the negative electrode is R 扩 ", then:

[0162] The total impedance value R of the battery s : R 总 = |(V3 - V1) / I| = |(3.2142 - 3.3065) / 3.194| * 1000 = 28.90mΩ; (*1000 is for unit conversion, V / A gives Ω)

[0163] The impedance sum R of the battery s + R 电 : R s + R 电 = |(V2 - V1) / I| = |(3.2565 - 3.3065) / 3.194| * 1000 = 15.65mΩ;

[0164] The diffusion impedance R of the battery 扩 : R 扩 = R 总 - (R s + R 电 ) = 28.90 - 15.65 = 13.25mΩ;

[0165] The electrochemical reaction impedance R of the battery 电 : R 电 = (R s + R 电 ) - R s = 15.65 - 5.3 = 10.35mΩ;

[0166] The total impedance value R of the positive electrode 总 ’: R 总 ’ = |(V6 - V4) / I| = |(3.3805 - 3.422) / 3.194| * 1000 = 12.99mΩ;

[0167] The impedance sum R of the positive electrode s ’ + R 电 ’: R s ’ + R 电 ’ = |(V5 - V4) / I| = |(3.404 - 3.422) / 3.194| * 1000 = 5.64mΩ;

[0168] The diffusion impedance R of the positive electrode 扩 ’: R 扩 ’ = R 总 ’ - (R s ’ + R电 ’) = 12.99 - 5.64 = 7.35 mΩ;

[0169] The total impedance value R of the negative electrode 总 ": R 总 " = |(V9 - V7) / I| = |(0.178 - 0.128) / 3.194| * 1000 = 15.65 mΩ;

[0170] The impedance sum R of the negative electrode s " + R 电 ": R s " + R 电 " = |(V8 - V7) / I| = |(0.160 - 0.128) / 3.194| * 1000 = 10.02 mΩ;

[0171] The diffusion impedance R of the negative electrode 扩 ": R 扩 " = R 总 " - (R s " + R 电 ") = 15.65 - 10.02 = 5.63 mΩ.

[0172] Example 2 (compared with Example 1, the voltage recording time interval is 0.5 s both during the static and pulsed discharge processes)

[0173] This example is basically the same as Example 1, except that:

[0174] S3 is: The battery with 50% SOC obtained in step S2 is first statically placed at room temperature (25 °C) for 1 h to ensure that the battery reaches an equilibrium state. Subsequently, it is statically placed at room temperature (25 °C) for a second time for 1 min. During both the first and second static placement processes, the voltage of the battery, the voltage of the positive electrode, and the voltage of the negative electrode are recorded every 0.5 s. The voltage of the battery in the last 0.5 s of the second static placement process is recorded as V1, the voltage of the positive electrode in the last 0.5 s of the second static placement process is recorded as V4, and the voltage of the negative electrode in the last 0.5 s of the second static placement process is recorded as V7.

[0175] Among them, V1 = 3.3065 V, V4 = 3.422 V, V7 = 0.128 V.

[0176] S4. Pulse discharge the battery that has been left standing twice in step S3 at room temperature (25°C) for 10 s with a current of 2C0. During the pulse discharge process, record the voltage of the battery, the voltage of the positive electrode, and the voltage of the negative electrode every 0.5 s. Denote the current as I, the voltage of the battery at the first 0.5 s of the pulse discharge as V2, the voltage of the battery at the last 0.5 s of the pulse discharge as V3, the voltage of the positive electrode at the first 0.5 s of the pulse discharge as V5, the voltage of the positive electrode at the last 0.5 s of the pulse discharge as V6, the voltage of the negative electrode at the first 0.5 s of the pulse discharge as V8, and the voltage of the negative electrode at the last 0.5 s of the pulse discharge as V9.

[0177] Among them, I = 2C0 = 3.194 A, V2 = 3.2483 V, V3 = 3.2142 V, V5 = 3.3995 V, V6 = 3.3805 V, V8 = 0.1635 V, V9 = 0.178 V.

[0178] Example 3 (compared with Example 1, the preset SOC is different)

[0179] This example is basically the same as Example 1, except that:

[0180] In step S2, charge and adjust the battery after the constant volume test in step S1 to 20% SOC with a current of 1C0.

[0181] Other differences are shown in Table 1 and Table 2.

[0182] Example 4 (compared with Example 1, pulse charging replaces pulse discharging)

[0183] This example is basically the same as Example 1, except that:

[0184] In step S4, use pulse charging instead of pulse discharging.

[0185] Other differences are shown in Table 1 and Table 2.

[0186] Example 5 (compared with Example 1, the pulse discharge current is 4C0)

[0187] This example is basically the same as Example 1, except that:

[0188] In step S4, pulse discharge the battery that has been left standing twice in step S3 at room temperature (25°C) for 10 s with a current of 4C0, where I = 4C0 = 6.388 A.

[0189] Other differences are shown in Table 1 and Table 2.

[0190] Example 6 (compared with Example 1, the pulse discharge time is 30 s)

[0191] This embodiment is basically the same as Embodiment 1, except that:

[0192] In step S4, the battery that has been left standing twice in step S3 is subjected to pulsed discharge at room temperature (25°C) for 30 s with a current of 2C0, where I = 2C0 = 3.194 A.

[0193] Other differences are shown in Tables 1 and 2.

[0194] Embodiment 7 (compared with Embodiment 1, the applicable temperature environment of the test method is different - low temperature and the pulsed current is 0.33C0)

[0195] This embodiment is basically the same as Embodiment 1, except that:

[0196] Steps S1, S2, S3, and S4 are all carried out at -10°C, and in step S4, the battery that has been left standing twice in step S3 is subjected to pulsed discharge at -10°C for 10 s with a current of 0.33C0, where I = 0.33C0 = 0.5530 A.

[0197] Other differences are shown in Tables 1 and 2.

[0198] Embodiment 8 (compared with Embodiment 1, the battery is a sodium-ion battery)

[0199] This embodiment is basically the same as Embodiment 1, except that:

[0200] In step S1, the battery is a sodium-ion battery.

[0201] Other differences are shown in Tables 1 and 2.

[0202] Comparative Example 1

[0203] The lithium-ion battery in step S1 of Embodiment 1 is subjected to EIS testing. Among them, the battery is adjusted to 50% SOC according to the S1 - S2 steps in Embodiment 1, and the EIS spectrum is fitted to obtain the ohmic impedance and electrochemical reaction impedance of the battery.

[0204] Comparative Example 2

[0205] The impedance test method of this comparative example includes the following steps:

[0206] a. The battery is fully charged at a current of 0.33C at room temperature (25°C); the battery is the battery in Embodiment 1

[0207] b. Discharge at 0.33C to 50% SOC at room temperature (25°C);

[0208] c. Stand still at room temperature (25°C) for 1 h;

[0209] d. Perform a 10s charge and discharge pulse test at a constant current of 1C under normal temperature (25°C) conditions;

[0210] Record the voltage after the third step of standing for 1h as V1’, the starting voltage of the fourth step of discharging at a constant current of 1C for 10s as V2’, the ending voltage as V3’, and the 1C constant current as I’. Then DCR = |(V3’ - V1’) / I’|; Decompose the DCR (Direct Current Resistance) of the whole process, where Rsei + Rct = |(V3’ - V2’) / I’|, Rsei is the interface impedance of the solid electrolyte interface (SEI), Rct is the charge transfer impedance, and DCR is also R in Example 1. 总 。

[0211] Comparative Example 3 (compared with Example 1, the voltage recording time interval is 1s for both the standing and pulse discharge processes)

[0212] This example is basically the same as Example 1, the differences are as follows:

[0213] S3: Let the battery with 50% SOC obtained in step S2 stand at normal temperature (25°C) for the first 1h to ensure that the battery reaches an equilibrium state. Subsequently, stand at normal temperature (25°C) for the second 1min. During both the first standing and the second standing processes, record the voltage of the battery, the voltage of the positive electrode, and the voltage of the negative electrode every 1s. Record the voltage of the battery at the last 1s of the second standing process as V1, record the voltage of the positive electrode at the last 1s of the second standing process as V4, and record the voltage of the negative electrode at the last 1s of the second standing process as V7.

[0214] Among them, V1 = 3.3065V, V4 = 3.422V, V7 = 0.128V.

[0215] S4: Perform a 10s pulse discharge on the battery that has undergone two standing processes in step S3 at a current of 2C0 at normal temperature (25°C). During the pulse discharge process, record the voltage of the battery, the voltage of the positive electrode, and the voltage of the negative electrode every 1s. Denote the current as I, denote the voltage of the battery at the first 1s of the pulse discharge as V2, denote the voltage of the battery at the last 1s of the pulse discharge as V3, denote the voltage of the positive electrode at the first 1s of the pulse discharge as V5, denote the voltage of the positive electrode at the last 1s of the pulse discharge as V6, denote the voltage of the negative electrode at the first 1s of the pulse discharge as V8, and denote the voltage of the negative electrode at the last 1s of the pulse discharge as V9.

[0216] Among them, I = 2C0 = 3.194A, V2 = 3.2434V, V3 = 3.2142V, V5 = 3.397V, V6 = 3.3805V, V8 = 0.165V, V9 = 0.178V.

[0217] The key test parameters involved in each example and comparative example are shown in Table 1.

[0218] Table 1 Key test parameters involved in each example and comparative example

[0219]

[0220]

[0221] Note: In Table 1, S represents an example, for example, S1 represents Example 1; D represents a comparative example, for example, D1 represents Comparative Example 1; the units of I and I’ are both A, and the units of V1, V2, V3, V4, V5, V6, V7, V8, V9, V1’, V2’, and V3’ are all V.

[0222] The impedance test results of each example and comparative example are shown in Table 2.

[0223] Table 2 Impedance test results of each example and comparative example

[0224]

[0225] Note: In Table 1, S represents an example, for example, S1 represents Example 1; D represents a comparative example, for example, D1 represents Comparative Example 1.

[0226] It can be seen from Table 2 that:

[0227] Compared with the comparative examples, the impedance test method of each example of the present application can not only measure the overall impedance of the battery, but also measure the impedance of the positive electrode and the negative electrode, and can further obtain the impedance of each part of the battery, the positive electrode, and the negative electrode through decomposition (for example, the ohmic impedance, the electrochemical reaction impedance, and the diffusion impedance of the battery, and the sum of the diffusion impedance, the ohmic impedance, and the electrochemical reaction impedance of the positive and negative electrodes), which is beneficial to in-depth analysis of the internal electrochemical process of the battery and is of great significance for battery optimization and battery failure analysis.

[0228] Comparing the results of Example 1 with Comparative Examples 1, 2, and 3, it can be seen that the DCR impedance decomposition results provided by the present application are basically consistent with the impedance decomposition results obtained by EIS fitting, with an error ≤ 1 mΩ, indicating that the DCR impedance test method provided by the present application is reasonable and accurate. And Rsei + Rct obtained in Comparative Example 2 (i.e., R 电 ) is 15.49 mΩ, and R 电 obtained in Comparative Example 3 is 14.46 mΩ, which differs greatly from the impedance result of 10.82 mΩ obtained by EIS fitting (error ≥ 3.5 mΩ), indicating that both the DCR decomposition method in Comparative Example 2 and the time interval of 1 s in Comparative Example 3 will lead to large errors in the test results.

[0229] Comparing the results of Comparative Examples 1 and 2 and Comparative Example 1, it can be seen that the DCR impedance decomposition results provided by the present application are basically consistent with the impedance decomposition results obtained by EIS fitting. When the time interval is 0.1 s, the error ≤ 0.5 mΩ, and when the time interval is 0.5 s, the error ≤ 2.1 mΩ, indicating that when the time interval is 0.1 s, the test results are accurate.

[0230] Through the analysis of the results of Example 1, it can be known that during the discharge process, the impedance of the graphite / silicon negative electrode dominates, indicating that the main factor affecting the discharge kinetic performance is the graphite / silicon negative electrode. Further DCR decomposition results show that for the lithium iron phosphate positive electrode, the diffusion impedance dominates, which is consistent with the relatively small lithium ion diffusion coefficient of lithium iron phosphate (generally between 10 -14 -10 -18 ; for graphite, it is between 10 -11 -10 -10 ). For the graphite / silicon negative electrode, the ohmic impedance and the electrochemical reaction impedance dominate. Since the ohmic impedance of the negative electrode is known to be small, it can be analyzed that the electrochemical reaction impedance should dominate, which is consistent with the structure of the silicon material. The poor contact between the deposited nano-silicon and the porous carbon matrix limits the rate of the electrochemical reaction. The DCR results are in good agreement with the actual situation of the system, indicating that the impedance test method provided by the present application is reasonable and accurate.

[0231] Through the analysis of the results of Example 3, it can be seen that at 20% SOC, the impedance of the lithium iron phosphate positive electrode dominates, indicating that at low SOC, the lithium iron phosphate positive electrode has a greater impact on the kinetic performance. And at low SOC, both the charge transfer impedance (i.e., R_electric in the present invention) and the diffusion impedance (i.e., R 扩 ) will increase significantly, which is consistent with the DCR decomposition results.

[0232] Through the analysis of the results of Examples 1 and 4, it can be seen that the charge / discharge process has little effect on the impedance of the negative electrode. However, during the charging process (i.e., lithium deintercalation from the positive electrode), the impedance of the lithium iron phosphate positive electrode increases significantly. Through DCR decomposition, it can be further determined that the diffusion impedance increases significantly, which is mainly related to the carbon coating layer on the surface of the lithium iron phosphate positive electrode. The carbon coating layer generally has a large external opening and a small internal opening, so it is more conducive to lithium intercalation (i.e., discharge) and less conducive to lithium deintercalation (i.e., charging). The test results are consistent with the actual situation.

[0233] Through the analysis of the results of Examples 1 and 5, it can be seen that when the pulsed discharge current increases to 4C, the impedance of the negative electrode is basically not affected, and the diffusion impedance of the lithium iron phosphate positive electrode decreases. This may be related to the increase in temperature under high current. The increase in temperature will cause the lithium ion diffusion to become faster. In addition, at high current density, the concentration gradient of lithium ions on the electrode surface increases, and the driving force is enhanced, which is conducive to the intercalation of lithium ions.

[0234] From the result analysis of Examples 1 and 6, it can be seen that when the pulse time increases to 30 s, the diffusion impedance of both the positive electrode and the negative electrode increases slightly, which may be related to the weakening of the driving force of the diffusion process under long time.

[0235] From the result analysis of Example 7, it can be seen that under low temperature conditions, the impedance of both the positive electrode and the negative electrode increases significantly, and the electrochemical reaction impedance is the dominant factor, which is mainly related to the increase of the charge transfer impedance under low temperature, in line with the facts.

[0236] From the result analysis of Example 8, it can be seen that in the sodium ion battery system, the impedance of the positive electrode is the dominant factor, which is mainly related to the small electronic conductivity and diffusion coefficient of the material, in line with the facts.

[0237] It can be seen from the above examples and comparative examples that the results obtained by the DCR impedance test method provided by the present invention are in line with the facts, and the test results have a small error from the generally recognized EIS method, indicating that the impedance test method provided by the present invention is reasonable and accurate.

[0238] In this application, the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of this application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0239] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first" and "second" can explicitly or implicitly include at least one of the features. In the description of this application, "a plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0240] Although the embodiments of this application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limiting this application. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of this application.

Claims

1. A method for testing impedance, characterized in that, Including: Performing a constant volume test on the battery to obtain a first battery; Adjusting the first battery to a preset state of charge (SOC) at a first constant current to obtain a second battery; Letting the second battery stand and recording a first voltage of the second battery after standing to obtain a third battery; Performing pulsed charging or pulsed discharging on the third battery at a second constant current, and recording a second voltage of the third battery after the start of the pulsed charging or pulsed discharging and a third voltage of the third battery at the end; Obtaining the ohmic impedance of the third battery, taking the absolute value of the ratio of the difference between the third voltage and the first voltage to the second constant current as the total impedance value of the third battery, taking the absolute value of the ratio of the difference between the second voltage and the first voltage to the second constant current as the impedance sum of the third battery, the impedance sum of the third battery being the sum of the ohmic impedance of the third battery and the electrochemical reaction impedance of the third battery, taking the difference between the total impedance value of the third battery and the impedance sum of the third battery as the diffusion impedance of the third battery, and taking the difference between the impedance sum of the third battery and the ohmic impedance of the third battery as the electrochemical reaction impedance of the third battery.

2. The test method according to claim 1, wherein The battery is a three - electrode battery, the three - electrode battery includes a secondary battery; and / or, the reference electrode of the three - electrode battery includes one of a lithium electrode, a lithium - plated electrode, a sodium electrode, and a sodium - plated electrode; and / or, during the testing process of the battery impedance testing method, the battery is placed in a battery test cabinet, and the voltages between the positive electrode and the reference electrode and between the negative electrode and the reference electrode are recorded through a multi - channel recorder.

3. The test method according to claim 2, wherein The battery impedance testing method further includes: Recording a fourth voltage of the positive electrode after standing; Recording a fifth voltage of the positive electrode after the start of the pulsed charging or pulsed discharging and a sixth voltage of the positive electrode at the end; Taking the absolute value of the ratio of the difference between the sixth voltage and the fourth voltage to the second constant current as the total impedance value of the positive electrode, taking the absolute value of the ratio of the difference between the fifth voltage and the fourth voltage to the second constant current as the impedance sum of the positive electrode, the impedance sum of the positive electrode being the sum of the ohmic impedance of the positive electrode and the electrochemical reaction impedance of the positive electrode, and taking the difference between the total impedance value of the positive electrode and the impedance sum of the positive electrode as the diffusion impedance of the positive electrode.

4. The test method according to claim 2, characterized in that The battery impedance testing method further includes: Recording a seventh voltage of the negative electrode after standing; Recording an eighth voltage of the negative electrode after the start of the pulsed charging or pulsed discharging and a ninth voltage of the negative electrode at the end; Taking the absolute value of the ratio of the difference between the ninth voltage and the seventh voltage to the second constant current as the total impedance value of the negative electrode, taking the absolute value of the ratio of the difference between the eighth voltage and the seventh voltage to the second constant current as the impedance sum of the negative electrode, the impedance sum of the negative electrode being the sum of the ohmic impedance of the negative electrode and the electrochemical reaction impedance of the negative electrode, and taking the difference between the total impedance value of the negative electrode and the impedance sum of the negative electrode as the diffusion impedance of the negative electrode.

5. The test method according to any one of claims 2 to 4, characterized in that, During the static state, during the pulse charging or discharging process, the voltage of the battery, the voltage of the positive electrode, and the voltage of the negative electrode are recorded in real time; and / or, The first voltage is the voltage of the second battery that reaches an equilibrium state after standing; and / or, The first voltage is the voltage of the second battery at the end of the first preset time during standing; and / or, The second voltage is the voltage of the third battery at the beginning of the second preset time during pulse charging or pulse discharging; and / or, The third voltage is the voltage of the third battery at the end of the third preset time during pulse charging or pulse discharging; and / or, The fourth voltage is the voltage of the positive electrode at the end of the fourth preset time during standing; and / or, The fifth voltage is the voltage of the positive electrode at the beginning of the fifth preset time during pulse charging or pulse discharging; and / or, The sixth voltage is the voltage of the positive electrode at the end of the sixth preset time during pulse charging or pulse discharging; The seventh voltage is the voltage of the negative electrode at the end of the seventh preset time during standing; and / or, The eighth voltage is the voltage of the negative electrode at the beginning of the eighth preset time during pulse charging or pulse discharging; and / or, The ninth voltage is the voltage of the negative electrode at the end of the ninth preset time during pulse charging or pulse discharging.

6. The test method according to claim 5, wherein The first preset time, the second preset time, the third preset time, the fourth preset time, the fifth preset time, the sixth preset time, the seventh preset time, the eighth preset time, and the ninth preset time are all 0.05 - 0.5 s, preferably 0.1 s.

7. The test method according to claim 1, characterized in that, The constant volume test of the battery includes: performing charge and discharge cycles on the battery; and / or, The method of adjusting the first battery to a preset SOC with a first constant current includes charging or / and discharging; and / or, The preset SOC is 0 - 100% SOC; Preferably, in the constant volume test, the rate used is 0.2C - 0.33C, and the number of cycles is 2 - 3 times; and / or, in the constant volume test, the discharge capacity of the last cycle of the battery is used as the capacity of the battery after the constant volume test.

8. The testing method according to claim 1, wherein The ratio of the first constant current to the capacity of the battery after the constant volume test is (0.2 - 1):1; and / or, The ratio of the second constant current to the capacity of the battery after the constant volume test is (0.2 - 5):1; and / or, The time of pulse charging or pulse discharging is 10 - 60 s; and / or, The standing includes a first standing and a second standing performed in sequence.

9. The test method according to claim 1, characterized in that The ratio of the second constant current to the capacity of the battery after the constant volume test is (2 - 3):1; and / or, The time of pulse charging or pulse discharging is 10 s; and / or, The time of the first standing is 0.5 - 1.5 h; and / or, The time of the second standing is 30 s to 90 s.

10. Application of the impedance test method according to any one of claims 1 to 9 in the field of secondary batteries.

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