Electrochemical impedance spectroscopy measurement method and system

Abstract

The invention relates to the technical field of electrochemical analysis, in particular to an electrochemical impedance spectroscopy measurement method and system. The method comprises the following steps: selecting any mode to measure an impedance value based on a measurement requirement: in the mode 1, generating an alternating-current excitation signal and a first direct-current bias voltage through a measurement chip, applying the alternating-current excitation signal and the first direct-current bias voltage to an electrochemical module, and calculating a response current to obtain the impedance value; the mode 2 is combined with a proportional method for measurement, and an impedance value is obtained through comparison and calculation of response current of a first reference resistor and an electrochemical module; according to the mode 3, a direct-current voltage signal is generated through the micro-control module and amplified by the differential amplification circuit to form a second direct-current bias voltage, the direct-current bias voltage and the alternating-current excitation signal are coupled and superposed through the constant-potential circuit to form a composite signal, the composite signal is applied to the electrochemical module, and response current is calculated to obtain an impedance value; and mode 4: applying a composite signal to the electrochemical module and the second reference resistor through a constant potential circuit, and calculating the response current in combination with a proportional method to obtain an impedance value.

Description

Technical Field

[0001] The present invention relates to the technical field of electrochemical analysis, and in particular to an electrochemical impedance spectroscopy measurement method and system. Background Art

[0002] Electrochemical impedance spectroscopy (EIS) is an important analytical technique that characterizes the dynamic behavior of electrode interfaces by applying a small-amplitude AC perturbation signal and measuring the system's response. Due to its non-destructive nature, high sensitivity, and rich information dimensionality, EIS technology has been widely used in fields such as lithium-ion battery state-of-health (SOH) assessment, biosensor detection (such as glucose and DNA), corrosion monitoring, and environmental pollutant analysis. However, as applications expand towards miniaturization and high frequencies, traditional EIS systems face multiple challenges: wide bandwidth (0.1Hz-1MHz), high precision (<1% error), and real-time performance (second-level response).

[0003] However, in electrochemical research, impedance spectroscopy measurements often rely on potentiostats. Existing commercial potentiostats with EIS functionality are expensive and require high maintenance and repair costs. Their complex internal structure and proprietary technology contribute to high operating costs. Furthermore, the hardware and software systems of these devices are not open source and utilize proprietary technologies. This closed system architecture makes it difficult for users to customize and expand the functionality of the devices according to their needs, significantly limiting experimental flexibility and innovation, and making it difficult to meet the diverse needs of small and medium-sized laboratories, educational settings, and other scenarios. Although numerous small potentiostats have been released, most lack EIS functionality. Some custom-made potentiostats that do include EIS functionality suffer from significant deficiencies in measurement accuracy and stability, severely impacting the reliability and reproducibility of experimental data and limiting their application in high-precision electrochemical research. Furthermore, the EIS function of custom-made potentiostats often suffers from a limited scanning frequency range, making it impossible to fully explore the dynamic behavior of electrochemical systems at different time scales, making it difficult to meet diverse experimental research needs. Summary of the Invention

[0004] To address at least one of the above-mentioned shortcomings of the prior art EIS, the present invention provides an electrochemical impedance spectroscopy measurement method, comprising selecting one of the following modes for electrochemical impedance measurement based on the DC bias requirement applied to the electrochemical module to be measured and the impedance measurement accuracy requirement: Mode 1: The measurement chip generates an AC excitation signal and a first DC bias voltage and applies them to the electrochemical module to generate a response current. The measurement chip then detects and calculates the response current to obtain an impedance value. Mode 2: Combined with the ratiometric measurement method, the impedance value is calculated by comparing the first reference resistor with the response current of the electrochemical module to be measured; Mode 3: A DC voltage signal is generated by the microcontroller module and amplified by a differential amplifier circuit to form a second DC bias voltage. The first and second DC bias voltages are then coupled and superimposed with the AC excitation signal by a constant potential circuit to form a composite signal, which is applied to the electrochemical module. The response current of the electrochemical module is detected and calculated by the measurement chip to obtain the impedance value. Mode 4: The composite signal is applied to the electrochemical module to be measured and the second reference resistor through a constant potential circuit, and the impedance value is obtained by comparing the response current of the second reference resistor and the electrochemical module to be measured in combination with the proportional method.

[0005] In some embodiments, the measurement chip integrates an ADC, a DAC, a waveform generator, and an impedance measurement circuit, and is used to generate an AC excitation signal and a first DC bias voltage, detect a response current, and calculate an impedance value. The model of the measurement chip is AD5941.

[0006] In some embodiments, the constant potential circuit includes an adder and a plurality of voltage followers for coupling the first DC bias voltage, the second DC bias voltage and the AC excitation signal.

[0007] In some embodiments, in Mode 2, the ratiometric measurement includes: Applying the same excitation signal to the first reference resistor and the electrochemical module to be measured; Obtaining the real part and the imaginary part of the response current of the first reference resistor and the electrochemical module to be measured respectively through discrete Fourier transform; Impedance value is calculated based on the formula: ; ; ; Where, is the impedance amplitude, 、 an impedance amplitude calculated from the real and imaginary parts of the resistance values of the first reference resistor and the electrochemical module to be measured, respectively; is the impedance phase, is the phase of the first reference resistor, is the phase of the electrochemical module to be tested, 、 are the real and imaginary parts of the resistance value of the first reference resistor, 、 are the real and imaginary parts of the resistance value of the electrochemical module to be measured.

[0008] In Mode 4, the ratiometric measurement includes: applying the same composite signal to the second reference resistor and the electrochemical module to be measured; Obtaining the real part and the imaginary part of the response current of the second reference resistor and the electrochemical module to be measured respectively through discrete Fourier transform; Impedance value is calculated based on the formula: ; ; ; Where, is the impedance amplitude, 、 an impedance amplitude calculated as the real and imaginary parts of the resistance values of the second reference resistor and the electrochemical module to be measured, respectively; is the impedance phase, is the phase of the first reference resistor, is the phase of the electrochemical module to be tested, 、 are the real and imaginary parts of the resistance value of the second reference resistor, 、 are the real and imaginary parts of the resistance value of the electrochemical module to be measured.

[0009] In some embodiments, different measurement modes are further switched through a mode switching module; the mode switching module includes a jumper cap and a control relay, and the jumper cap is used to realize the impedance value measurement switching between mode 1 and mode 2; the jumper cap and the control relay work together to realize the impedance value measurement switching between mode 3 and mode 4.

[0010] In some embodiments, during the measurement process of mode 2, a first switching circuit is also used to connect to a first reference resistor with different impedance values so as to enable the first reference resistor to switch to different resistance value ranges; during the measurement process of mode 4, a second switching circuit is also used to enable the second reference resistor to switch to different resistance value ranges; the second switching circuit includes multiple groups of resistance switching relays, and the multiple groups of resistance switching relays are respectively connected to second reference resistors with different impedance values.

[0011] In some embodiments, the differential amplifier circuit is electrically connected to the microcontroller module and the constant potential circuit, respectively, and the differential amplifier circuit includes at least a voltage reference chip U13 and a differential amplifier U14A; in mode 3 and mode 4, after a DC voltage signal is generated by the microcontroller module, the DC voltage signal is amplified to a range of ±9V by the differential amplifier circuit to form a second DC bias voltage and input into the constant potential circuit.

[0012] In some embodiments, the microcontroller module includes an STM32.

[0013] An embodiment of the present invention further provides an electrochemical impedance spectroscopy measurement system, comprising a microcontroller module, a measurement chip, an electrochemical module, a constant potential circuit, a first reference resistor, a second reference resistor, and a constant potential circuit; The microcontroller module is used to select different measurement modes for electrochemical impedance value measurement based on the DC bias requirement and impedance measurement accuracy requirement applied to the electrochemical module to be measured, and the measurement modes include mode 1, mode 2, mode 3, and mode 4; The measuring chip is electrically connected to the electrochemical module to implement mode 1, wherein the measuring chip generates an AC excitation signal and a first DC bias voltage and applies them to the electrochemical module to generate a response current, and the measuring chip detects and calculates the response current to obtain an impedance value; The measuring chip is electrically connected to the first reference resistor to implement mode 2, which is a ratiometric measurement method in which the impedance value is obtained by comparing the first reference resistor with the response current of the electrochemical module to be measured; The measuring chip is electrically connected to the electrochemical module via a constant potential circuit, and the microcontroller is electrically connected to the constant potential circuit via a differential amplifier circuit to implement mode 3. Mode 3 is to generate a DC voltage signal via the microcontroller, and amplify the DC voltage signal via the differential amplifier circuit to form a second DC bias voltage. The first DC bias voltage, the second DC bias voltage and the AC excitation signal are then coupled and superimposed with the constant potential circuit to form a composite signal, which is then applied to the electrochemical module. The response current of the electrochemical module is detected and calculated by the measuring chip to obtain an impedance value. The measurement chip is also electrically connected to a second reference resistor via a constant potential circuit, and the second reference resistor is electrically connected to a mode switching module to implement mode 4. Mode 4 applies a composite signal to the electrochemical module to be measured and the second reference resistor via the constant potential circuit, and combines the proportional method to measure, and calculates the impedance value by comparing the response current of the second reference resistor with that of the electrochemical module to be measured.

[0014] In some embodiments, the measurement chip is AD5941, and the microcontroller module includes STM32.

[0015] Based on the above, compared with the existing technology, the electrochemical impedance spectroscopy measurement method provided by the present invention not only effectively broadens the frequency range while improving the measurement accuracy and stability through the effective design of multiple modes and the calculation of impedance values in combination with the proportional method, but also adapts to applications with different working conditions.

[0016] Other features and beneficial effects of the present invention will be described in the following description, and in part will become apparent from the description, or will be understood by practicing the present invention. The objectives and other beneficial effects of the present invention can be achieved and obtained by the structures particularly pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, a brief introduction will be given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work. The positional relationships described in the drawings in the following description are based on the directions of the components drawn in the diagrams, unless otherwise specified.

[0018] Figure 1 A circuit block diagram of an electrochemical impedance spectroscopy measurement method provided in one embodiment of the present invention; Figure 2 A circuit block diagram of an electrochemical impedance spectroscopy measurement method provided by another embodiment of the present invention; Figure 3 This is the circuit diagram of AD5941; Figure 4 This is the circuit diagram of the differential amplifier circuit; Figure 5 The figure is a circuit diagram showing the connection between the adder, voltage follower and electrochemical module in the constant potential circuit; Figure 6 This is the circuit diagram of the mode switching module; Figure 7 is a circuit diagram for connecting a first switching circuit and a first reference resistor; Figure 8 FIG. 4 is a circuit diagram showing the connection between the second switching circuit and the second reference resistor. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments; the technical features designed in different implementation modes of the present invention described below can be combined with each other as long as they do not conflict with each other; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0020] In the description of the present invention, it should be noted that all terms used in the present invention (including technical terms and scientific terms) have the same meanings as those generally understood by ordinary technicians in the field to which the present invention belongs, and should not be understood as limiting the present invention; it should be further understood that the terms used in the present invention should be understood to have the same meanings as these terms in the context of this specification and the relevant field, and should not be understood in an idealized or overly formal sense, unless explicitly defined as such in the present invention.

[0021] Common impedance measurement methods currently include the bridge method, the resonance method, the IV method, and the auto-balancing bridge method. The bridge method requires manual balancing, which is complex and inefficient. Parasitic parameters significantly affect high frequencies (>1 MHz), making it suitable only for low frequencies (<100 kHz) and small impedance ranges. The resonance method only supports single-frequency measurements, requiring point-by-point retuning for wideband sweeps, which is time-consuming and unable to capture dynamic characteristics. Component loss and tuning errors can easily lead to reduced accuracy, typically worse than ±5%. It is only suitable for passive devices with distinct resonant characteristics (such as inductors and capacitors) and is poorly suited for complex impedance scenarios such as bioimpedance. The IV method, under high-frequency excitation (>100 kHz), introduces amplitude and phase errors due to distributed lead parameters (such as stray capacitance), requiring additional compensation algorithms. The dynamic range is limited (typically 1:1000), and the signal-to-noise ratio drops sharply at extreme impedances (<10 mΩ or >10 GΩ). The auto-balancing bridge method, however, is susceptible to interference at extreme impedances (such as low-resistance contact resistance and high-resistance leakage current). Its high-frequency stability is limited by feedback delay, leading to high equipment costs. Furthermore, most current home-made EIS systems utilize the auto-balancing bridge method, which measures the response current in constant voltage mode. This method has limitations such as a limited frequency range, insufficient system stability, and low accuracy.

[0022] Therefore, in response to the limitations of the above-mentioned existing electrochemical impedance spectroscopy measurement methods in terms of measurement accuracy, system stability, frequency response, and anti-interference ability, the present invention provides an electrochemical impedance spectroscopy measurement method, which aims to achieve a wider frequency range measurement, higher measurement accuracy and flexibility, and is easier for users to customize and expand according to specific applications.

[0023] The following describes in detail and in conjunction with specific embodiments a method for measuring electrochemical impedance spectroscopy provided by the present invention. Figure 1 The electrochemical impedance spectroscopy measurement method provided by one embodiment of the present invention includes at least the following: selecting one of the following modes for electrochemical impedance measurement based on the DC bias requirements applied to the electrochemical module to be measured and the impedance measurement accuracy requirements: Mode 1: The measurement chip generates an AC excitation signal and a first DC bias voltage and applies them to the electrochemical module to generate a response current. The measurement chip then detects and calculates the response current to obtain an impedance value. Mode 2: Combined with the ratiometric measurement method, the impedance value is calculated by comparing the first reference resistor with the response current of the electrochemical module to be measured; Mode 3: A DC voltage signal is generated by the microcontroller module and amplified by a differential amplifier circuit to form a first DC bias voltage. The first and second DC bias voltages are then coupled and superimposed with an AC excitation signal by a constant potential circuit to form a composite signal, which is applied to the electrochemical module. The response current of the electrochemical module is detected and calculated by a measurement chip to obtain an impedance value. Mode 4: The composite signal is applied to the electrochemical module to be measured and the second reference resistor through a constant potential circuit, and the impedance value is obtained by comparing the response current of the second reference resistor and the electrochemical module to be measured in combination with the proportional method.

[0024] The method for selecting one of the following modes for electrochemical impedance measurement based on the DC bias requirements applied to the electrochemical module to be measured and the impedance measurement accuracy requirements can be to pre-set a preset DC bias threshold and a preset DC bias threshold using the microcontroller module, and the microcontroller module automatically selects the mode based on the preset thresholds. The specific thresholds can be reasonably set according to actual operating conditions and are not limited here.

[0025] Its mode selection logic can be: when the applied DC bias is less than or equal to the preset DC bias threshold of the measurement chip and the required impedance value accuracy is less than or equal to the preset impedance value accuracy threshold, select mode 1 to perform electrochemical impedance value measurement; when the applied DC bias is less than or equal to the preset DC bias threshold of the measurement chip and the required impedance value accuracy is greater than the preset impedance value accuracy threshold, select mode 2 to perform electrochemical impedance value measurement; when the applied DC bias is greater than the preset DC bias threshold of the measurement chip and the required impedance value accuracy is less than or equal to the preset impedance value accuracy threshold, select mode 3 to perform electrochemical impedance value measurement; when the applied DC bias is greater than the preset DC bias threshold of the measurement chip and the required impedance value accuracy is greater than the preset impedance value accuracy threshold, select mode 4 to perform electrochemical impedance value measurement.

[0026] For example, when the AD5941 is used as the measurement chip, since the DC bias generated by the AD5941 is no greater than 2.2V, the preset DC bias threshold of the AD5941 is set to 2.2V. If the DC bias is ≤2.2V and the accuracy requirement is ≤5%, select Mode 1; if the DC bias is ≤2.2V and the accuracy requirement is >5%, select Mode 2; if the DC bias is >2.2V and the accuracy requirement is ≤5%, select Mode 3; if the DC bias is >2.2V and the accuracy requirement is >5%, select Mode 4. It should be noted that the preset DC bias threshold should not exceed the maximum DC bias value that the measurement chip can generate. The specific values of the preset DC bias threshold and the impedance value accuracy threshold can be reasonably designed based on the actual measurement chip model and its component requirements, and this embodiment does not limit them here.

[0027] Of course, according to the present invention, those skilled in the art can also select a corresponding mode for electrochemical impedance measurement based on actual experience, and it is not necessary to completely rely on the preset threshold to automatically select the mode.

[0028] It should also be noted that the specific implementation of each mode can be designed using existing conventional circuits or computer programs according to specific functions, and will not be described in detail here.

[0029] Further, see Figure 2 、 Figure 3 The measurement chip integrates an ADC, a DAC, a waveform generator, and an impedance measurement circuit, and is used to generate an AC excitation signal and a first DC bias voltage, detect the response current, and calculate the impedance value. For example, in this embodiment, the preferred measurement chip model is the AD5941. The AD5941 is a high-precision analog front-end chip that integrates a high-resolution ADC, a DAC, an impedance measurement circuit, and signal conditioning functions, supporting various measurement modes such as electrochemical impedance spectroscopy (EIS) and potentiostat. Specifically, the digital waveform generator within the AD5941 chip can generate a sinusoidal excitation signal with a DC bias ranging from 0.015 Hz to 200 kHz, which is output to the electrochemical module via the CE0 pin. Simultaneously, the response current of the electrochemical module can be input via the AD5941 chip's AIN1 pin and converted to a digital signal by the internal 16-bit ADC. Furthermore, the AD5941 chip includes a built-in DFT hardware accelerator that analyzes and calculates the real and imaginary parts of the digital signal, directly outputting the impedance magnitude. Of course, other measurement chip models that meet the aforementioned requirements may also be used.

[0030] Specifically, the AD5941 measurement chip is used as an example to provide instructions for implementing measurements in various measurement modes.

[0031] Mode 1 is the direct measurement mode, which generates an AC excitation signal and a first DC bias voltage through the AD5941 internal waveform generator and applies them directly to the counter electrode (CE) of the electrochemical module through the CE0 pin. The response current returns to the AIN1 pin of the AD5941 through the working electrode (WE) and is converted into a digital signal by the internal 16-bit ADC. The AD5941 has a built-in DFT hardware accelerator to extract the real part of the response current. and the imaginary part , calculate the impedance amplitude of the electrochemical module , that is, using AD5941 to independently complete signal generation, detection and impedance value calculation.

[0032] Mode 2 is the proportional measurement mode. When the accuracy of the measured electrochemical impedance value is required to be high, the proportional measurement method can be used for measurement. The proportional measurement method includes: first applying the same excitation signal to the first reference resistor and the electrochemical module to be measured; then obtaining the real and imaginary parts of the response current of the first reference resistor and the electrochemical module to be measured respectively through discrete Fourier transform; finally, calculating the impedance value based on the formula.

[0033] Specifically, the AD5941 applies the same AC excitation signal and first DC bias voltage to the first reference resistor and the electrochemical module to be tested, that is, the AD5941 applies the AC excitation signal and the first DC bias voltage directly to the counter electrode (CE) of the electrochemical module through the CE0 pin, and also applies the AC excitation signal and the first DC bias voltage to the first reference resistor through the RCAL0 pin. The response current of the electrochemical module returns to the AIN1 pin of the AD5941 through the working electrode (WE), and the response current of the first reference resistor returns to the RCAL1 pin of the AD5941. Then, the built-in DFT of the AD5941 extracts the real part of the response current of the electrochemical module and the imaginary part and the real part of the response current of the first reference resistor and the imaginary part , calculate the impedance value, where the impedance value includes impedance amplitude and impedance phase. The specific formula includes: ; ; ; Where, is the impedance amplitude, 、 The impedance amplitudes are calculated as the real and imaginary parts of the resistance values of the first reference resistor and the electrochemical module to be measured, respectively; that is, , . is the impedance phase, is the phase of the first reference resistor, is the phase of the electrochemical module to be tested, 、 are the real and imaginary parts of the resistance value of the first reference resistor, 、 are the real and imaginary parts of the resistance value of the electrochemical module to be measured.

[0034] Mode 3 is a DC bias-coupled measurement mode. Specifically, the AD5941's internal waveform generator generates an AC excitation signal and a first DC bias voltage. However, due to its limited internal DC bias, when a larger bias is required on the electrochemical system, the microcontroller in Mode 3 generates a DC voltage signal and inputs it through the DC output port to a differential amplifier circuit. This DC voltage signal is amplified by the differential amplifier circuit to form a second DC bias voltage. A potentiostat circuit then superimposes the AD5941's AC excitation signal, the first DC bias voltage, and the second DC bias voltage to form a composite signal, thus meeting the larger bias requirement. Similarly, after applying the composite signal to the electrochemical module's counter electrode (CE), the subsequent steps are similar to those in Mode 1. The response current from the electrochemical module returns to the AD5941's AIN1 pin via the working electrode (WE) and is converted to a digital signal by the internal 16-bit ADC. The AD5941's built-in DFT hardware accelerator extracts the real and imaginary components of the response current and calculates the impedance of the electrochemical module.

[0035] Mode 4 is a high-precision DC bias ratio method mode. When a large DC bias needs to be applied while improving the impedance measurement accuracy, the DC bias and ratio method can be used to measure the impedance value of the electrochemical module. Specifically, a DC voltage signal is also generated by the microcontroller module, and the DC voltage signal is amplified by the differential amplifier circuit to form a second DC bias voltage. The AC excitation signal generated by the measurement chip, the first DC bias voltage, and the second DC bias voltage are then superimposed with the help of a constant potential circuit to form a composite signal. Next, the same composite signal is applied to the first reference resistor and the electrochemical module to be measured; the real and imaginary parts of the response current of the second reference resistor and the electrochemical module to be measured are then obtained respectively through discrete Fourier transform; finally, the impedance value is calculated based on the formula.

[0036] Specifically, the AC excitation signal and the first DC bias voltage generated by AD5941 are input into the constant potential circuit through the CE0 pin. The DC voltage signal generated by the microcontroller module is input into the differential amplifier circuit through the DC output port. The differential amplifier circuit amplifies the DC voltage signal to form a second DC bias voltage. The AC excitation signal is then coupled and superimposed with the first DC bias voltage and the second DC bias voltage by means of the constant potential circuit to form a composite signal, which is applied to the counter electrode (CE) and the second reference resistor on the electrochemical module respectively. Subsequently, in the same manner as mode 2, the response current of the electrochemical module returns to the AIN1 pin of AD5941 through the working electrode (WE), and the response current of the second reference resistor returns to the AIN1 pin of AD5941. The built-in DFT of AD5941 extracts the real part of the response current of the electrochemical module respectively. , imaginary part and the real part of the response current of the second reference resistor , imaginary part , and calculate the impedance value, where the impedance value includes impedance amplitude and impedance phase. The specific formula includes: ; ; ; Where, is the impedance amplitude, 、 The impedance amplitudes are calculated as the real and imaginary parts of the resistance values of the second reference resistor and the electrochemical module to be measured, respectively; that is, , , is the impedance phase, is the phase of the first reference resistor, is the phase of the electrochemical module to be tested, 、 are the real and imaginary parts of the resistance value of the second reference resistor, 、 are the real and imaginary parts of the resistance value of the electrochemical module to be measured.

[0037] The microcontroller is electrically connected to the constant potential circuit via a differential amplifier circuit. The microcontroller may include an MCU or other processor. In this embodiment, the microcontroller preferably includes an STM32, such as the STM32H743ZGT6. Preferably, the control module is provided with a communication interface for communicating with a host computer and transmitting corresponding control instructions and data information. In this embodiment, the microcontroller is also connected to the measurement chip via SPI communication, so as to transmit corresponding control instructions and data information between the microcontroller and the measurement chip to achieve impedance value measurement in each mode.

[0038] Preferably, the differential amplifier circuit is electrically connected to the microcontroller module and the constant potential circuit, respectively. In the above-mentioned modes 3 and 4, a DC voltage signal is generated by the microcontroller module and input into the differential amplifier circuit through the DC output port. The DC voltage signal is amplified to a range of ±9V by the differential amplifier circuit to form a second DC bias voltage, which is then input into the constant potential circuit. At the same time, the constant potential circuit is also used to receive the AC excitation signal and the first DC bias voltage generated by the measurement chip, and couple and superimpose the three to obtain a composite signal.

[0039] It should be noted that the microcontroller module, measurement chip, electrochemical module, constant potential circuit, first reference resistor, second reference resistor, and constant potential circuit mentioned in the above method can all be designed using existing reasonable circuits or computer programs according to the above specific functions, and the corresponding circuit and program designs all fall within the scope of protection of the embodiments of the present invention.

[0040] To effectively illustrate the circuit connection relationship of the hardware in the electrochemical impedance spectroscopy measurement method provided in the above embodiment, the hardware structure of each circuit module is described below by taking the measurement chip using AD5941 and the microcontroller module including STM32 as an example.

[0041] The constant potential circuit includes an adder and several voltage followers, which are used to couple the first and second DC bias voltages with the AC excitation signal. The differential amplifier circuit includes at least a voltage reference chip U13 and a differential amplifier U14A, which amplifies the DC voltage signal generated by the STM32 and forms the second DC bias voltage.

[0042] Specifically, see Figure 4 The differential amplifier circuit includes a voltage reference chip U13, a differential amplifier U14A, and several surrounding resistors and capacitors. Among them, the voltage reference chip U13 can increase the standard reference voltage of 3V and 1.5V. The 1.5V reference voltage can be used as the reverse input voltage of the differential amplifier U14A, and the non-inverting input voltage of the differential amplifier U14A comes from the DAC1 output port of the STM32, which outputs a 0-3V analog signal (i.e., a DC voltage signal). After passing through the differential amplifier U14A, the 0-3V analog signal can be amplified to ±9V, and the output analog signal of the differential amplifier U14A can be used as the input of the second DC bias voltage in mode 3 and mode 4.

[0043] See also Figure 5The constant potential circuit also includes an adder U10A, a voltage follower U9A, a voltage follower U10B, and a voltage follower U9B. The inverting input of adder U10A is connected to the outputs of voltage followers U9A, U10B, and U9B, respectively. The output of adder U10A is connected to the counter electrode (CE1) of the electrochemical module. The non-inverting input of voltage follower U9A is connected to the measurement chip to receive the AC excitation signal and the first DC bias voltage. Specifically, the non-inverting input of voltage follower U9A is connected to the CE0 pin of the AD5941. The non-inverting input of voltage follower U10B is electrically connected to the differential amplifier circuit, specifically, to the output of differential amplifier U14A, to receive the second DC bias voltage. The non-inverting input of voltage follower U9B is connected to the reference electrode (RE1) of the electrochemical module.

[0044] Based on the above circuit connection, voltage follower U9A, which receives the AC excitation signal and the first DC bias voltage, and voltage follower U10B, which receives the second DC bias voltage, have high input impedance for signal absorption and low output impedance. They can drive loads to isolate the front- and back-stage circuits, preventing current fluctuations in the back-stage circuit from affecting the stability of the front-stage signal source. Adder U10A couples the AC excitation signal with the first and second DC bias voltages. Voltage follower U9B utilizes the high input impedance and low output impedance characteristics of the op amp to transmit the reference electrode's potential undistorted to the inverting input of adder U10A, which controls the op amp. This maintains a constant potential difference between the working and reference electrodes, keeping the applied potential constant and achieving a constant potential function.

[0045] In an optional embodiment, the electrochemical impedance spectroscopy measurement method also includes switching different measurement modes through a mode switching module; the mode switching module includes a jumper cap and a control relay, and the jumper cap is used to realize the impedance value measurement switching between mode 1 and mode 2; the jumper cap and the control relay work together to realize the impedance value measurement switching between mode 3 and mode 4.

[0046] When implementing it specifically, Figure 6 As shown, jumper cap J6 connects the measurement chip and constant potential circuit, respectively, to control whether only the measurement chip is active or whether the constant potential circuit is switched. Control relay RY7 connects the second reference resistor, the microcontroller module, and the measurement chip. The microcontroller module transmits a control signal to control relay RY7 to determine whether the impedance value of the second reference resistor should be measured when the constant potential circuit is active.

[0047] That is, when the 1-2 pins and 5-6 pins of the jumper cap J6 are connected, the measurement chip is activated to enable mode 1; when the pins of the reference resistor corresponding to the jumper cap J5 are connected, mode 2 is enabled; when the 3-4 pins and 7-8 pins of the jumper cap J6 are connected and the control relay RY7 is in the normally open state, the measurement chip and the constant potential circuit are activated, and a composite signal is applied to the electrochemical module to enable mode 3; when the 3-4 pins and 7-8 pins of the jumper cap J6 are connected and the control relay RY7 is energized and closed, it is switched to enable mode 4, so that the measurement chip, the constant potential circuit are activated, and the second reference resistor is turned on, and the second reference resistor and the electrochemical module are measured respectively.

[0048] According to the above-mentioned inventive concept, those skilled in the art may also adopt other switching switches or components or other circuit connection relationships to realize the switching of the above-mentioned four modes, which all fall within the protection scope of the present invention.

[0049] In another optional embodiment, during the measurement process of mode 2, a first switching circuit is further used to connect to a first reference resistor with different impedance values so as to enable the first reference resistor to switch to different resistance value ranges; during the measurement process of mode 4, a second switching circuit is further used to enable the second reference resistor to switch to different resistance value ranges; the second switching circuit includes multiple groups of resistance switching relays, and the multiple groups of resistance switching relays are respectively connected to second reference resistors with different impedance values.

[0050] Specifically, when using Mode 2 and Mode 4 combined with the ratiometric method to measure the impedance of an electrochemical module, theoretically, the closer the resistance of the electrochemical module is to the reference resistor, the smaller the error, and the more accurate the measured impedance value of the electrochemical module. Therefore, to maximize the range of impedance values and improve the accuracy of the measured impedance values, this embodiment utilizes a first switching circuit and a second switching circuit to respectively switch between the different resistance values of the first and second reference resistors.

[0051] As an example, see Figure 7 The first switching circuit is connected to the RCAL0 and RCAL1 pins of the AD5941, respectively. The first switching circuit may include a jumper cap J5 and a plurality of first reference resistors having different resistance values. Jumper cap J5 may be used to switch between first reference resistors having different resistance values. For example, first reference resistors having multiple resistance levels, such as 10Ω, 50Ω, 100Ω, 500Ω, 1KΩ, and 5KΩ, may be set for switching. Of course, other resistance value ranges may also be selected based on implementation requirements.

[0052] See also Figure 8 ,The second switching circuit includes multiple groups of resistance switching relays, such as Figure 8Relays RY1 through RY6 in the circuit diagram each have multiple sets of resistance switching relays connected to corresponding second reference resistors with different impedance values. Each set of resistance switching relays is connected to a second reference resistor to enable switching between first reference resistors with different resistance values. For example, multiple resistance ranges of second reference resistors with different resistance values, such as 10Ω, 50Ω, 100Ω, 500Ω, 1000Ω, and 5000Ω, can be set for switching. Of course, other resistance value ranges can also be selected based on implementation requirements.

[0053] By switching reference resistors of different resistance values as described above, the accuracy of the measured impedance value can be effectively improved, further increasing the applicable scope of electrochemical impedance spectroscopy measurement.

[0054] According to the inventive concept, those skilled in the art may also use connections of other circuit elements to implement switching control of the reference resistor, such as a sliding rheostat, which all fall within the protection scope of the present invention.

[0055] Based on the above, the electrochemical impedance spectroscopy measurement method provided by the embodiment of the present invention can switch the impedance measurement mode according to different test requirements. When the electrochemical impedance spectroscopy test only requires a small DC bias and the accuracy requirement is not high, the impedance measurement can be directly performed using the measurement chip; if there is a requirement for accuracy, the impedance can be measured using the measurement chip combined with the proportional method, which can effectively improve the measurement accuracy; if a large DC bias needs to be applied during the measurement process, the AC disturbance and DC bias can be coupled with the adder in the constant potential circuit and then applied to the electrochemical module, and finally the response current can be directly measured using the measurement chip and the impedance value can be calculated; if a large DC bias is applied and higher accuracy is also required, the impedance measurement can also be performed using the constant potential circuit combined with the proportional method.

[0056] Among them, the advantage of using the proportional method combined with the constant voltage mode to measure the electrochemical impedance spectrum is that it can improve the measurement accuracy, that is, the proportional method can effectively eliminate systematic errors such as amplitude fluctuations of the signal source, phase offsets, and gain changes of the measurement system. This method reduces the errors caused by the signal source and the measurement system itself by comparing the amplitude and phase of the current, thereby improving the accuracy and reliability of the measurement. In addition, the proportional method simplifies the calculation process. Since only the change in current needs to be paid attention to, there is no need to process the measurement data of voltage and current at the same time. It is also suitable for measuring electrochemical cells with different impedance ranges, because the measurement results do not depend on the absolute values of voltage and current, but are calculated by the relative change of current. Even in the case of large changes in impedance, accurate measurement results can be obtained.

[0057] The present invention also provides an electrochemical impedance spectroscopy measurement system, which comprises at least a microcontroller module, a measurement chip, an electrochemical module, a constant potential circuit, a first reference resistor, a second reference resistor, and a constant potential circuit; The microcontroller module is used to select different measurement modes for electrochemical impedance value measurement based on the DC bias requirement and impedance measurement accuracy requirement applied to the electrochemical module to be measured, and the measurement modes include mode 1, mode 2, mode 3, and mode 4; The measuring chip is electrically connected to the electrochemical module to implement mode 1, wherein the measuring chip generates an AC excitation signal and a first DC bias voltage and applies them to the electrochemical module to generate a response current, and the measuring chip detects and calculates the response current to obtain an impedance value; The measuring chip is electrically connected to the first reference resistor to implement mode 2, which is a ratiometric measurement method in which the impedance value is obtained by comparing the first reference resistor with the response current of the electrochemical module to be measured; The measurement chip is electrically connected to the electrochemical module via a constant potential circuit, and the microcontroller is electrically connected to the constant potential circuit via a differential amplifier circuit to implement Mode 3. Mode 3 is a process in which the microcontroller generates a DC voltage signal, amplifies the DC voltage signal via the differential amplifier circuit to form a second DC bias voltage, and then couples and superimposes the first and second DC bias voltages with an AC excitation signal via the constant potential circuit to form a composite signal, which is applied to the electrochemical module. The measurement chip detects and calculates the response current of the electrochemical module to obtain an impedance value. The measurement chip is also electrically connected to a second reference resistor via a constant potential circuit, and the second reference resistor is electrically connected to a mode switching module to implement mode 4. Mode 4 applies a composite signal to the electrochemical module to be measured and the second reference resistor via the constant potential circuit, and combines the proportional method to measure, and calculates the impedance value by comparing the response current of the second reference resistor with that of the electrochemical module to be measured.

[0058] The electrochemical impedance spectroscopy measurement system further includes a mode switching module, a first switching circuit, and a second switching circuit. The constant potential circuit includes an adder and several voltage followers. The differential amplifier circuit includes a voltage reference chip and a differential amplifier. The specific functions and structures of each module and circuit can be found in the above-mentioned method embodiment and are not further described here.

[0059] In summary, compared with the prior art, the electrochemical impedance spectroscopy measurement method and system provided by the present invention have the following advantages: 1. The cost of implementing electrochemical impedance spectroscopy measurements based on a measurement chip is low. The integrated ADC, DAC, and waveform generator within the measurement chip greatly reduces the difficulty of hardware design. Furthermore, the output of excitation signals and detection of response signals are achieved on the same chip, avoiding problems such as signal coupling distortion caused by multi-module discrete designs. Second, by adopting four mode switching, the impedance value with a frequency range of 0.015HZ~200KHZ can be measured, which effectively improves the frequency range of the existing homemade impedance system. Different measurement modes can be switched according to different impedance measurement requirements, effectively improving the versatility under different working conditions. Third, in constant voltage mode, the impedance of the actual electrochemical module is measured using a ratiometric method combined with the impedance value of a reference resistor. This effectively eliminates system errors, reduces signal distortion and noise that may be caused during signal processing, and improves measurement accuracy. It also avoids the significant limitations of EIS applications caused by using only conventional constant current mode. 4. Compared with other impedance measurement solutions implemented using the AD5941 chip, the method and system provided in this embodiment combine a constant potential circuit, the DAC output port of the microcontroller module, and a voltage reference chip to increase the DC bias voltage that can be applied to the electrochemical module, thereby effectively increasing the DC bias of the impedance system and broadening its application scope and scenarios.

[0060] In addition, those skilled in the art should understand that, although there are many problems in the prior art, each embodiment or technical solution of the present invention may be improved in only one or several aspects, without having to simultaneously solve all the technical problems listed in the prior art or background art. Those skilled in the art should understand that any content not mentioned in a claim should not be construed as limiting the claim.

[0061] Although terms such as microcontroller module, measurement chip, electrochemical module, constant potential circuit, first reference resistor, second reference resistor, and constant potential circuit are frequently used herein, the use of other terms is not excluded. These terms are used solely to more conveniently describe and explain the essence of the present invention; interpreting them as any additional limitations is contrary to the spirit of the present invention. In the description and claims of the embodiments of the present invention, and in the accompanying drawings, the terms "first" and "second" (if any) are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for measuring electrochemical impedance spectroscopy, characterized in that: include: Based on the DC bias requirements and impedance measurement accuracy requirements for the electrochemical module to be measured, select one of the following modes for electrochemical impedance measurement: Mode 1: The measurement chip generates an AC excitation signal and a first DC bias voltage and applies them to the electrochemical module to generate a response current. The measurement chip then detects and calculates the response current to obtain an impedance value. Mode 2: Combined with the ratiometric measurement method, the impedance value is calculated by comparing the first reference resistor with the response current of the electrochemical module to be measured; Mode 3: A DC voltage signal is generated by the microcontroller module and amplified by a differential amplifier circuit to form a second DC bias voltage. The first and second DC bias voltages are then coupled and superimposed with the AC excitation signal by a constant potential circuit to form a composite signal, which is applied to the electrochemical module. The response current of the electrochemical module is detected and calculated by the measurement chip to obtain the impedance value. Mode 4: The composite signal is applied to the electrochemical module to be measured and the second reference resistor through a constant potential circuit, and the impedance value is obtained by comparing the response current of the second reference resistor and the electrochemical module to be measured in combination with the proportional method.

2. The electrochemical impedance spectroscopy measurement method according to claim 1, wherein: The measurement chip integrates an ADC, a DAC, a waveform generator and an impedance measurement circuit, and is used to generate an AC excitation signal and a first DC bias voltage, detect a response current and calculate an impedance value. The model of the measurement chip is AD5941.

3. The electrochemical impedance spectroscopy measurement method according to claim 1, wherein: The constant potential circuit includes an adder and a plurality of voltage followers, which are used for coupling a first DC bias voltage, a second DC bias voltage and an AC excitation signal.

4. The electrochemical impedance spectroscopy measurement method according to claim 1, characterized in that: In Mode 2, the ratiometric measurement includes: Applying the same excitation signal to the first reference resistor and the electrochemical module to be measured; Obtaining the real part and the imaginary part of the response current of the first reference resistor and the electrochemical module to be measured respectively through discrete Fourier transform; Impedance value is calculated based on the formula: ; ; ; Where, is the impedance amplitude, 、 an impedance amplitude calculated from the real and imaginary parts of the resistance values of the first reference resistor and the electrochemical module to be measured, respectively; is the impedance phase, is the phase of the first reference resistor, is the phase of the electrochemical module to be tested, 、 are the real and imaginary parts of the resistance value of the first reference resistor, 、 are the real and imaginary parts of the resistance value of the electrochemical module to be measured; In Mode 4, the ratiometric measurement includes: applying the same composite signal to the second reference resistor and the electrochemical module to be measured; Obtaining the real part and the imaginary part of the response current of the second reference resistor and the electrochemical module to be measured respectively through discrete Fourier transform; Impedance value is calculated based on the formula: ; ; ; Where, is the impedance amplitude, 、 an impedance amplitude calculated as the real and imaginary parts of the resistance values of the second reference resistor and the electrochemical module to be measured, respectively; is the impedance phase, is the phase of the first reference resistor, is the phase of the electrochemical module to be tested, 、 are the real and imaginary parts of the resistance value of the second reference resistor, 、 are the real and imaginary parts of the resistance value of the electrochemical module to be measured.

5. The electrochemical impedance spectroscopy measurement method according to claim 1, wherein: It also includes switching different measurement modes through a mode switching module; the mode switching module includes a jumper cap and a control relay, and the jumper cap is used to realize the impedance value measurement switching between mode 1 and mode 2; the jumper cap and the control relay work together to realize the impedance value measurement switching between mode 3 and mode 4.

6. The electrochemical impedance spectroscopy measurement method according to claim 1, wherein: During the measurement process of mode 2, a first switching circuit is also used to connect to a first reference resistor with different impedance values so as to enable the first reference resistor to switch to different resistance value ranges; during the measurement process of mode 4, a second switching circuit is also used to enable the second reference resistor to switch to different resistance value ranges; the second switching circuit includes multiple groups of resistance switching relays, and the multiple groups of resistance switching relays are respectively connected to second reference resistors with different impedance values.

7. The electrochemical impedance spectroscopy measurement method according to claim 1, wherein: The differential amplifier circuit is electrically connected to the microcontroller module and the constant potential circuit respectively, and the differential amplifier circuit includes at least a voltage reference chip U13 and a differential amplifier U14A; in mode 3 and mode 4, after a DC voltage signal is generated by the microcontroller module, the DC voltage signal is amplified to a range of ±9V by the differential amplifier circuit to form a second DC bias voltage and input into the constant potential circuit.

8. The electrochemical impedance spectroscopy measurement method according to claim 1, wherein: The microcontroller module includes STM32.

9. An electrochemical impedance spectroscopy measurement system, characterized in that: It includes a microcontroller module, a measuring chip, an electrochemical module, a constant potential circuit, a first reference resistor, a second reference resistor, and a constant potential circuit; The microcontroller module is used to select different measurement modes for electrochemical impedance value measurement based on the DC bias requirement and impedance measurement accuracy requirement applied to the electrochemical module to be measured, and the measurement modes include mode 1, mode 2, mode 3, and mode 4; The measuring chip is electrically connected to the electrochemical module to implement mode 1, wherein the measuring chip generates an AC excitation signal and a first DC bias voltage and applies them to the electrochemical module to generate a response current, and the measuring chip detects and calculates the response current to obtain an impedance value; The measuring chip is electrically connected to the first reference resistor to implement mode 2, which is a ratiometric measurement method in which the impedance value is obtained by comparing the first reference resistor with the response current of the electrochemical module to be measured; The measurement chip is electrically connected to the electrochemical module via a constant potential circuit, and the microcontroller is electrically connected to the constant potential circuit via a differential amplifier circuit to implement Mode 3. Mode 3 is a process in which the microcontroller generates a DC voltage signal, amplifies the DC voltage signal via the differential amplifier circuit to form a second DC bias voltage, and then couples and superimposes the first and second DC bias voltages with an AC excitation signal via the constant potential circuit to form a composite signal, which is applied to the electrochemical module. The measurement chip detects and calculates the response current of the electrochemical module to obtain an impedance value. The measurement chip is also electrically connected to a second reference resistor via a constant potential circuit, and the second reference resistor is electrically connected to a mode switching module to implement mode 4. Mode 4 applies the composite signal to the electrochemical module to be measured and the second reference resistor via the constant potential circuit, and combines the proportional method to measure, and calculates the impedance value by comparing the response current of the second reference resistor with that of the electrochemical module to be measured.

10. The electrochemical impedance spectroscopy measurement system according to claim 9, characterized in that: The model of the measurement chip is AD5941, and the microcontroller module includes STM32.

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