A method, system, medium, and product for testing a laminated three-electrode lithium-ion battery

Abstract

The application discloses a kind of lamination three-electrode lithium ion battery test method, system, medium and product, it is related to the field of measuring electric variable, in the method, by applying positive and negative alternating two-way disturbance test current to the battery in static state, wherein the current absolute value and duration of forward charging pulse are equal to negative discharge pulse.The voltage of battery terminal is collected, the ratio of the polarization amplitude of positive and negative is defined as the kinetic asymmetry coefficient.The coefficient is compared with the preset intrinsic symmetry reference value, when the kinetic asymmetry coefficient is greater than the reference value, it is determined that lithium precipitation exists in the battery.The application is used to reduce the interference of current collector electronic ohmic voltage drop on measurement data under high rate working condition, improve the accuracy of negative electrode potential monitoring, so as to improve the accuracy of determining lithium precipitation critical threshold.

Description

Technical Field

[0001] This application belongs to the field of measuring electrical variables, and in particular relates to a testing method, system, medium and product for stacked three-electrode lithium-ion batteries. Background Technology

[0002] When exploring the limits of performance and safety boundaries for large-capacity lithium-ion power batteries manufactured using a stacking process, researchers need to accurately grasp the electrochemical behavior of the positive and negative electrodes within the battery, especially the potential change of the negative electrode during charging, to prevent lithium plating. Traditional two-electrode testing systems can only obtain the terminal voltage between the positive and negative electrodes. This voltage is a coupled result of the positive electrode potential, the negative electrode potential, and the ohmic voltage drop inside the battery. When faced with complex electrochemical reaction processes, the two-electrode system cannot isolate the independent potential information of the negative electrode side, making it difficult to determine the lithium plating critical point of the battery under specific operating conditions, thus limiting the full release of the battery's fast-charging capability.

[0003] A widely used technology in related fields is the implanted three-electrode testing technique. This typically involves placing an extremely thin metal wire (such as lithium-plated gold or copper wire) as a reference electrode at the geometric center of the stacked battery cell, within the separator layer between the positive and negative electrodes. After insulation treatment, this reference electrode is led out of the battery casing, providing a relatively stable potential reference point for the testing system. This allows the testing equipment to monitor the voltages of the positive and negative electrodes relative to the reference electrode, thus decomposing the full-cell voltage into two half-cell voltages. This provides intuitive data support for analyzing the internal polarization impedance distribution and phase transition processes of the electrode materials. Furthermore, traditional special R&D batteries with reference electrodes rely heavily on manual processes during fabrication. For example, copper wire with a diameter of approximately 10 micrometers is typically soaked in concentrated sulfuric acid overnight to remove the surface oxide layer. Then, the positive electrode, separator, copper wire, separator, and negative electrode are manually placed sequentially, followed by three-sided sealing. This entire process suffers from significant efficiency bottlenecks, requiring manual intervention at approximately 10 points, making it cumbersome. More importantly, manual operation has serious inconsistencies, resulting in poor sample repeatability and affecting the consistency and reliability of battery performance testing.

[0004] When applying a high current of up to 3C or 4C to the battery for continuous constant current charging test, the current is injected through the tab bus and diffuses along the originally very thin current collector metal foil towards the center of the electrode. Due to the physical existence of an objective electronic resistance in the current collector foil of large-size stacked batteries, when an ampere-hour-level high current flows through this path, an electronic ohmic voltage drop will be generated between the tab and the geometric center of the electrode. However, the reference electrode probe of the relevant technology is located at the center of the electrode, while the voltage sampling point is located at the external tab. This results in the "negative electrode-reference" potential data collected by the test system actually incorrectly superimposing the electronic ohmic voltage drop component on the current collector metal foil. This voltage component increases significantly with the increase of charging current, causing the measured negative electrode potential value to deviate from the true solid-liquid interface double layer potential, reducing the accuracy of the test system in judging the critical threshold of negative electrode lithium plating under fast charging conditions. Summary of the Invention

[0005] This application provides a testing method, system, medium, and product for stacked three-electrode lithium-ion batteries, which reduces the interference of current collector electronic ohmic voltage drop on measurement data under high-rate operating conditions, improves the accuracy of negative electrode potential monitoring, and thus improves the accuracy of determining the critical threshold for lithium plating.

[0006] In one aspect, this application provides a test method for stacked three-electrode lithium-ion batteries, which automates the assembly of lithium-ion batteries and stacks and seals them in the order of lower shell, negative electrode, first separator, reference electrode, second separator, positive electrode and upper shell.

[0007] The assembled lithium-ion battery was transferred to a test location that integrates a temperature chamber and a charge / discharge machine for in-situ testing. When the lithium-ion battery was in a static state, the control current loop applied a bidirectional disturbance test current to the lithium-ion battery. The bidirectional disturbance test current consisted of alternating positive charging pulses and negative discharging pulses in time sequence, and the absolute values ​​of the currents of the positive charging pulses and the negative discharging pulses were equal and the durations were equal.

[0008] The terminal voltage of the lithium-ion battery is continuously collected at a preset sampling frequency.

[0009] The forward polarization amplitude is calculated based on the terminal voltage. The forward polarization amplitude is the absolute value of the difference between the terminal voltage at the end of the forward charging pulse and the terminal voltage at the beginning of the forward charging pulse.

[0010] The negative polarization amplitude is calculated based on the terminal voltage. The negative polarization amplitude is the absolute value of the difference between the terminal voltage at the end of the negative discharge pulse and the terminal voltage at the beginning of the negative discharge pulse.

[0011] The ratio of the positive polarization amplitude to the negative polarization amplitude is used as the dynamic asymmetry coefficient;

[0012] Obtain a preset intrinsic symmetry reference value. The preset intrinsic symmetry reference value is the theoretical value of the kinetic asymmetry coefficient of the lithium-ion battery in the non-lithium-plated state, corresponding to the current temperature and state of charge.

[0013] If the kinetic asymmetry coefficient is determined to be greater than the preset intrinsic symmetry benchmark value, it is determined that lithium plating exists inside the lithium-ion battery.

[0014] By employing the above technical solution, a bidirectional perturbation test current is applied to a quiescent lithium-ion battery. The ratio of the positive and negative polarization amplitudes is calculated using the terminal voltage as a kinetic asymmetry coefficient, and compared with a preset intrinsic symmetry benchmark value to determine whether lithium plating exists in the battery. Since the positive charging pulse and negative discharging pulse of the bidirectional perturbation test current have equal absolute current values ​​and durations, the battery's charging and discharging states remain dynamically balanced during the test. The kinetic asymmetry coefficient reflects the asymmetry of the positive and negative electrode kinetic responses during charging and discharging. When lithium plating occurs, the deposition of metallic lithium leads to a significant enhancement in the kinetic response during charging, while the kinetic response during discharging is relatively weak, thus increasing the kinetic asymmetry coefficient. By comparing with the preset intrinsic symmetry benchmark value, the kinetic asymmetry phenomenon caused by lithium plating can be effectively identified, improving the accuracy and reliability of lithium plating detection in lithium-ion batteries, reducing the interference of current collector electronic ohmic voltage drop on measurement data under high-rate operating conditions, and improving the accuracy of negative electrode potential monitoring, thereby improving the accuracy of determining the critical threshold for lithium plating.

[0015] In conjunction with some implementations of the first aspect, in some implementations, the forward polarization amplitude is calculated based on the terminal voltage, specifically including:

[0016] Extract the transient voltage sequence within a preset time window at the instant the positive charging pulse is activated;

[0017] Calculate the time derivative of the transient voltage sequence and determine the Ohmic inflection point when the time derivative undergoes a step change.

[0018] Read the inflection point voltage value corresponding to the ohmic inflection point and use the inflection point voltage value as the pure ohmic response voltage;

[0019] Obtain the final voltage value at the end of the positive charging pulse;

[0020] The absolute value of the difference between the final voltage value and the pure ohmic response voltage is determined as the positive polarization amplitude.

[0021] By employing the above technical solution, this method analyzes the transient voltage sequence at the instant the forward charging pulse is activated, identifies the ohmic inflection point where the time derivative value undergoes a step change, obtains the pure ohmic response voltage, and uses the difference between the final voltage value at the end of the charging pulse and the pure ohmic response voltage as the forward polarization amplitude. This method separates the contributions of ohmic polarization and electrochemical polarization through the time derivative characteristics of the voltage response, making the calculation of the polarization amplitude more accurate. Since the characteristic time scale of the ohmic polarization response is much smaller than that of the electrochemical polarization, it manifests as an instantaneous voltage change when the current changes stepwise. Therefore, identifying the step characteristic of the voltage time derivative can accurately determine the ohmic inflection point. The polarization amplitude obtained after removing the influence of ohmic polarization can more accurately reflect the electrochemical polarization process, improving the calculation accuracy of the kinetic asymmetry coefficient. This time derivative-based analysis method reduces the influence of measurement noise and interference, improving the anti-interference capability of polarization amplitude measurement.

[0022] In conjunction with some implementations of the first aspect, in some implementations, the forward polarization amplitude is calculated based on the terminal voltage, specifically including:

[0023] The voltage values ​​of all sampling points during the duration of the forward charging pulse are obtained to construct the charging voltage response curve;

[0024] The charging voltage response curve was fitted to a preset electrochemical polarization index model using the least squares method. The preset electrochemical polarization index model includes a polarization voltage saturation term and a time constant term.

[0025] The asymptotic value of steady-state polarization voltage is calculated based on the fitted preset electrochemical polarization index model.

[0026] Obtain the initial open-circuit voltage value at the start of the positive charging pulse;

[0027] The absolute value of the difference between the steady-state asymptotic polarization voltage and the initial open-circuit voltage is determined as the positive polarization amplitude.

[0028] By employing the above technical solution, a charging voltage response curve is constructed by collecting voltage response data during the forward charging pulse. The curve is then fitted to a pre-defined electrochemical polarization exponential model containing a polarization voltage saturation term and a time constant term using the least squares method. The difference between the steady-state asymptotic polarization voltage and the initial open-circuit voltage is calculated as the forward polarization amplitude. This method considers the dynamic characteristics of the electrochemical polarization process, obtaining the steady-state characteristic values ​​of the polarization response through model fitting, thus avoiding the influence of sampling time on the measurement results. The polarization voltage saturation term in the exponential model reflects the equilibrium state of the polarization process, and the time constant term characterizes the polarization kinetic rate. Least squares fitting effectively suppresses the influence of measurement noise. The polarization amplitude calculated based on the asymptotic value is not limited by the measurement cutoff time, improving the consistency and repeatability of polarization amplitude measurement.

[0029] In conjunction with some implementation methods of the first aspect, in some implementation methods, the asymptotic value of the steady-state polarization voltage is calculated based on the fitted preset electrochemical polarization index model, specifically including:

[0030] The pre-defined functional expression for the electrochemical polarization index model is:

[0031] ;

[0032] in, For time Terminal voltage at time 10:00 The initial voltage, This is the pulse current value. For ohmic internal resistance, Let be the steady-state polarization amplitude parameters to be fitted. The time constant parameter to be fitted;

[0033] The charging voltage response curve is iteratively calculated using the least squares method to solve for the optimal parameters. and ;

[0034] Will and and Add them together to get The asymptotic value of the steady-state polarization voltage as it approaches infinity.

[0035] By employing the above technical solution, an electrochemical polarization index model function expression including initial voltage, ohmic internal resistance, polarization amplitude parameters, and time constant parameters is established. The charging voltage response curve is iteratively solved using the least squares method to obtain the optimal model parameters and calculate the steady-state asymptotic value of the polarization voltage. This method decomposes the battery voltage response into three parts: initial voltage, ohmic voltage drop, and polarization voltage, accurately describing the dynamic characteristics of the polarization process through a mathematical model. The least squares iterative solution process fully utilizes all sampled data, improving the stability of parameter estimation. The time constant parameter in the model reflects the polarization kinetic characteristics, aiding in the analysis of the rate characteristics of the polarization process. Calculating the asymptotic value of the polarization voltage based on the complete mathematical model improves the accuracy of polarization amplitude measurement and reduces measurement errors.

[0036] In conjunction with some embodiments of the first aspect, in some embodiments, after determining that lithium plating exists inside the lithium-ion battery, the method further includes:

[0037] Collect the relaxation terminal voltage sequence between the end of the forward charging pulse and the preset relaxation cutoff time;

[0038] Calculate the first-order differential sequence of the relaxor voltage sequence with respect to time;

[0039] To determine whether there are local maxima in a first-order differential sequence, a local maximum is the inflection point where the value of the first-order differential sequence changes from increasing to decreasing.

[0040] If a local maximum point exists in the first-order differential sequence, it confirms that lithium plating exists inside the lithium-ion battery.

[0041] If there are no local maxima in the first-order differential sequence and the first-order differential sequence decreases monotonically with time, then the lithium-ion battery is determined to be in a concentration polarization-dominated state.

[0042] By employing the above technical solution, and by acquiring the relaxation voltage sequence after the positive charging pulse ends and calculating its first-order differential sequence, two different physical processes—lithium plating and concentration polarization—can be identified from the dynamic changes in the voltage relaxation process. When lithium plating is present, the dissolution process introduces additional electrochemical reactions during relaxation, leading to a non-monotonic voltage relaxation curve, manifested as local maxima in the first-order differential sequence. In contrast, under pure concentration polarization, since only the diffusion of lithium ions in the electrolyte is involved, the voltage relaxation curve exhibits a smooth, monotonic change, with its first-order differential sequence decreasing monotonically over time. This discrimination method based on dynamic relaxation characteristics improves the accuracy of lithium plating detection and reduces the probability of misjudgment due to interference from other electrochemical processes.

[0043] In some embodiments, in conjunction with the first aspect, before determining that the lithium-ion battery is in a concentration polarization-dominated state, the method further includes:

[0044] Calculate the first-order differential of the first-order differential sequence with respect to time to obtain the second-order differential sequence;

[0045] Determine whether there is a local minimum in a second-order differential sequence. A local minimum is an inflection point where the value of the second-order differential sequence changes from decreasing to increasing.

[0046] If a local minimum point exists in the second-order differential sequence, it is determined that there is trace amount of lithium plating inside the lithium-ion battery or strong polarization masking lithium plating.

[0047] If there are no local minima in the second-order differential sequence, the lithium-ion battery is determined to be in a concentration polarization-dominated state.

[0048] By employing the aforementioned technical solution, and further calculating the second-order differential sequence of the voltage relaxation curve and analyzing its local minimum point characteristics, trace amounts of lithium plating or lithium plating phenomena masked by strong polarization can be detected. When trace amounts of lithium plating are present, although the first-order differential sequence may exhibit a monotonically decreasing trend, the lithium dissolution process will still leave weak characteristic traces on the voltage relaxation curve. These weak characteristics are amplified in the second-order differential sequence, manifesting as local minimum points. This detection method based on higher-order derivative analysis improves the detection sensitivity for trace lithium plating, reduces the false negative rate of lithium plating detection, and enables relatively accurate identification of lithium plating even when the battery is in a strongly polarized state.

[0049] In conjunction with some implementation methods of the first aspect, in some implementation methods, determining whether a local minimum point exists in the second-order differential sequence specifically includes:

[0050] Identify all candidate points for local minima in a second-order differential sequence;

[0051] Calculate the peak-valley depth corresponding to each candidate minimum point. The peak-valley depth is the absolute value of the difference between the candidate minimum point and the adjacent maximum point.

[0052] If the peak-valley depth of at least one candidate minimum point is greater than the preset feature significance threshold, then it is determined that there is a local minimum point in the second-order differential sequence.

[0053] By employing the above technical solution, and introducing peak-valley depth calculation and feature significance judgment into the second-order differential sequence, the true lithium plating characteristics can be effectively distinguished from fluctuations caused by noise. By calculating the absolute value of the difference between each candidate minimum point and its adjacent maximum point, and comparing it with a preset feature significance threshold, statistically significant feature points can be selected. This quantitative threshold-based judgment method improves the reliability of lithium plating detection, reduces the false detection rate caused by measurement noise and data fluctuations, and makes the lithium plating detection results more stable and repeatable.

[0054] In a second aspect, embodiments of this application provide a stacked three-electrode lithium-ion battery testing system, which includes: one or more processors and a memory; the memory is coupled to one or more processors, the memory is used to store computer program code, the computer program code includes computer instructions, and one or more processors call the computer instructions to cause the system to perform the method described in the first aspect and any possible implementation thereof.

[0055] Thirdly, embodiments of this application provide a computer-readable storage medium including instructions that, when executed on a system, cause the system to perform the method described in the first aspect and any possible implementation thereof.

[0056] Fourthly, embodiments of this application provide a computer program product that, when run on a system, causes the system to execute the method described in any possible implementation of the first aspect.

[0057] One or more technical solutions provided in the embodiments of this application have at least the following technical effects or advantages:

[0058] 1. This application provides a testing method for stacked three-electrode lithium-ion batteries. By applying a bidirectional perturbation test current to a quiescent lithium-ion battery, the ratio of the positive and negative polarization amplitudes is calculated as a kinetic asymmetry coefficient based on the terminal voltage. This coefficient is then compared with a preset intrinsic symmetry benchmark to determine whether lithium plating exists in the battery. Since the positive charging pulse and negative discharging pulse of the bidirectional perturbation test current have equal absolute current values ​​and durations, the charging and discharging states of the battery remain dynamically balanced during the test. The kinetic asymmetry coefficient reflects the asymmetry of the positive and negative electrode kinetic responses during charging and discharging. When lithium plating occurs, the deposition of metallic lithium leads to a significant enhancement in the kinetic response during charging, while the kinetic response during discharging is relatively weak, thus increasing the kinetic asymmetry coefficient. By comparing with a preset intrinsic symmetry benchmark, the kinetic asymmetry phenomenon caused by lithium plating can be effectively identified, improving the accuracy and reliability of lithium plating detection in lithium-ion batteries, reducing the interference of the current collector electronic ohmic voltage drop on measurement data under high-rate operating conditions, and improving the accuracy of negative electrode potential monitoring, thereby improving the accuracy of determining the critical threshold for lithium plating.

[0059] 2. This application provides a testing method for stacked three-electrode lithium-ion batteries. By acquiring the relaxation voltage sequence after the end of the forward charging pulse and calculating its first-order differential sequence, two different physical processes—lithium plating and concentration polarization—can be identified from the dynamic changes in the voltage relaxation process. When lithium plating is present, the dissolution process introduces additional electrochemical reactions during relaxation, resulting in a non-monotonic voltage relaxation curve, manifested as local maxima in the first-order differential sequence. In contrast, under pure concentration polarization, since only the diffusion process of lithium ions in the electrolyte is involved, the voltage relaxation curve exhibits a smooth, monotonic change, with its first-order differential sequence decreasing monotonically over time. This discrimination method based on relaxation dynamics improves the accuracy of lithium plating detection and reduces the probability of misjudgment due to interference from other electrochemical processes. Attached Figure Description

[0060] Figure 1 This is a schematic flowchart of a test method for a stacked three-electrode lithium-ion battery according to an embodiment of this application.

[0061] Figure 2This is another schematic flowchart of a test method for a stacked three-electrode lithium-ion battery according to an embodiment of this application.

[0062] Figure 3 This is a schematic diagram of the physical device structure of a stacked three-electrode lithium-ion battery testing system provided in an embodiment of this application. Detailed Implementation

[0063] The terminology used in the following embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. As used in the specification and appended claims of this application, the singular expressions “a,” “an,” “the,” “the,” “the,” and “this” are intended to include the plural expressions as well, unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used in this application refers to any or all possible combinations including one or more of the listed items.

[0064] Hereinafter, the terms "first" and "second" are used for descriptive purposes only and should not be construed as implying or suggesting relative importance or implicitly indicating the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature, and in the description of the embodiments of this application, unless otherwise stated, "multiple" means two or more.

[0065] The following example is used in conjunction with Figure 1 The present application describes a testing method for a stacked three-electrode lithium-ion battery in its embodiments:

[0066] Please see Figure 1 This is a flowchart illustrating a testing method for a stacked three-electrode lithium-ion battery according to an embodiment of this application.

[0067] S101. The lithium-ion battery is automatically assembled and stacked and sealed in the following order: lower shell, negative electrode, first separator, reference electrode, second separator, positive electrode and upper shell.

[0068] Automated assembly refers to the process of using mechanical equipment and control systems to replace manual labor in the precise alignment and stacking of battery components. This process is not limited to a specific type of robotic arm or control bus protocol. The lower casing refers to the bottom encapsulation structure that carries the internal battery components and provides basic physical support. The negative electrode is a conductive current collector coated with negative electrode active material, used to insert lithium ions during charging. The separator is an insulating film with a microporous structure, used to isolate the positive and negative electrodes to prevent physical short circuits while allowing lithium ions to permeate. The reference electrode is a third electrode that provides a stable reference potential, typically made from pre-treated copper wire or lithium iron phosphate electrode sheets. The positive electrode is a conductive current collector coated with positive electrode active material, used to de-intercalate and re-intercalate lithium ions during discharge. The upper casing refers to the outermost electrode structure or top encapsulation assembly. Sealing refers to enclosing the stacked components inside the casing through methods such as thermopressing or ultrasonic welding to isolate them from the external environment. In executing this step, the system completely eliminates the more than ten cumbersome operation steps of traditional manual processes. Through preset program instructions, it controls automated equipment to strictly follow the sequence of lower casing, negative electrode, separator, reference electrode, separator, positive electrode, and upper casing, sequentially picking up, aligning, and stacking materials, and immediately performing a sealing process after stacking. This automated, assembly-line operation significantly improves sample preparation efficiency, eliminates the inconsistencies caused by manual operation, and ensures a high degree of repeatability in the physical structure and initial electrochemical state of each fabricated special R&D battery with three electrodes.

[0069] To implement this step, the system can achieve high-precision stacking and sealing through various automated technologies. One specific implementation method is to use a multi-axis robotic arm collaborative assembly system guided by machine vision. This system is equipped with a high-resolution industrial camera and an image processing unit. After each component is grasped by the vacuum suction cup robotic arm, the image processing unit extracts the contour features of the component through an edge detection algorithm and compares them with a standard template to calculate the positional and rotational angle deviations. Subsequently, the control system drives the robotic arm to perform micron-level posture compensation based on the deviation values, ensuring that the geometric centers of each layer of components are strictly aligned on the stacking platform. Especially when placing reference electrodes with micron-level diameters, the vision system accurately positions the side area of ​​the battery and guides a special fixture to lay the reference electrode flat between the two layers of separators. After stacking, the hot-press sealing mold, driven by a servo motor, completes the edge sealing according to a preset pressure and temperature curve. Another implementation method is to use an automated production line combining modular fixtures and linear guide rails. The system is designed with modular fixtures with positioning pins and limiting grooves to achieve rapid sample loading and mechanical positioning. The feeding stations for each component are arranged sequentially along a linear guide rail, and the fixture carrying the lower housing moves stepwise along the rail. At each station, a pneumatic robot uses a mechanical limiting device to precisely push the corresponding electrode or diaphragm into the positioning slot of the fixture. At the reference electrode station, an automatic unwinding mechanism stretches and cuts the pre-treated reference electrode wire, attaching it to a predetermined position on the side via electrostatic adsorption or micro-airflow guidance. Finally, the fixture enters the ultrasonic welding station, where high-frequency vibration friction achieves molecular-level fusion sealing of the housing edges.

[0070] S102. The assembled lithium-ion battery is transferred to the test position that integrates the temperature chamber and the charge / discharge machine for in-situ testing. When the lithium-ion battery is in a static state, the control current loop applies a bidirectional disturbance test current to the lithium-ion battery.

[0071] Transfer refers to the physical movement of sealed battery samples from the assembly station to the testing station. A temperature chamber is a closed cavity device that provides precise temperature control and environmental simulation, used to provide a constant or alternating temperature field for battery testing. A charge / discharge machine is a power electronic testing device that can apply specific current or voltage excitation to the battery according to a preset program and measure the battery's electrical performance parameters with high precision. A testing location is a physical space or platform specifically used for performing electrochemical performance evaluation. In-situ testing refers to a testing method that directly monitors and analyzes the internal state and electrochemical reaction process of the battery in real time without damaging the battery structure or changing the battery's physical location and environmental conditions. After completing the above automated assembly, the system immediately executes the transfer command, sending the battery into the integrated testing platform that combines the temperature chamber and the charge / discharge machine. After entering the testing location, the battery can directly enter the in-situ testing stage after pretreatment processes such as lithium plating without secondary manual wiring or environmental adaptation.

[0072] When the lithium-ion battery is in a resting state, the system control current loop applies a bidirectional disturbance test current to the lithium-ion battery. This bidirectional disturbance test current consists of alternating positive charging pulses and negative discharging pulses in a time sequence, with the absolute current values ​​and durations of the positive charging pulse and negative discharging pulse being equal. A lithium-ion battery in a resting state means that the battery has not undergone charging or discharging operations within a preset time period, and its internal electrochemical reactions are in relative equilibrium, with the rate of change of terminal voltage below a preset voltage stability threshold. The current loop is a closed conductive path connecting the positive and negative terminals of the battery to an external load or power source, used to transmit electrical energy or test signals. The bidirectional disturbance test current is an excitation signal containing current components in both positive and negative directions, designed to disrupt the battery's electrochemical equilibrium state to stimulate its dynamic response. A positive charging pulse is a brief current process where the current flows from the outside to the positive terminal of the battery, causing lithium ions to deintercalate from the positive terminal and intercalate into the negative terminal; a negative discharging pulse is a brief current process where the current flows from the positive terminal to the outside, causing lithium ions to deintercalate from the negative terminal and intercalate into the positive terminal. The absolute value of the current refers to the magnitude of the current, regardless of the direction sign. The duration refers to the length of time the pulse current is maintained at the preset current value. After detecting that the lithium-ion battery meets the conditions for a resting state, the system injects a specific current waveform into the lithium-ion battery by controlling the power devices in the current loop. This current waveform has strict timing characteristics; that is, the positive charging pulse and the negative discharging pulse alternate in chronological order. Furthermore, to ensure that the battery's state of charge (SOC) does not significantly drift before and after the test, the system strictly controls the absolute values ​​of the positive charging pulse and the negative discharging pulse to be equal, and simultaneously controls their durations to be exactly equal. This symmetrical design aims to ensure that the total charge injected into the battery theoretically cancels out the total charge released from the battery, thereby achieving non-destructive or minimal-destructive testing of the battery.

[0073] To implement this step, the system can achieve precise application of bidirectional disturbance test current through various technical means. One specific implementation method utilizes a high-precision programmable bidirectional DC power supply system. This system integrates a bidirectional DC / DC converter and controls the duty cycle of power switching transistors (such as MOSFETs or IGBTs) through a digital signal processor (DSP). The system first sets the target current value and pulse width. The DSP generates a corresponding pulse width modulation (PWM) signal based on the set parameters, driving the bidirectional DC / DC converter to rapidly switch between source mode (charging) and load mode (discharging). In source mode, the system controls the output voltage to be higher than the battery voltage to generate a positive charging current; in load mode, the system controls the internal load to consume battery energy to generate a negative discharging current, and ensures that the rising and falling edges of the current waveform meet the preset slope requirements through closed-loop feedback control.

[0074] Another implementation uses a combined architecture of an independent electronic load and a programmable power supply. The system simultaneously controls the programmable power supply and the electronic load via a bus (such as CAN or RS485). When a positive pulse is generated, the system activates the power supply output and disconnects the electronic load; when a negative pulse is generated, the system shuts off the power supply output and activates the electronic load to draw current. The system coordinates the actions of the two devices through a high-precision timing controller, ensuring that the switching interval is within microseconds, thereby synthesizing the required bidirectional disturbance test current waveform.

[0075] S103. Continuously collect the terminal voltage of the lithium-ion battery at a preset sampling frequency;

[0076] The preset sampling frequency refers to the number of times the system digitizes the analog voltage signal per unit time. This frequency is typically set according to Shannon's sampling theorem and must be much higher than the characteristic frequency of the battery's electrochemical reaction to ensure complete capture of transient details of voltage changes. The terminal voltage of a lithium-ion battery refers to the potential difference between the positive and negative terminals. This value includes the battery's open-circuit voltage and the overpotential caused by ohmic internal resistance, electrochemical polarization, and concentration polarization. Continuous acquisition means that the system continuously acquires voltage data throughout the entire bidirectional disturbance test current application process, forming a continuous voltage data stream. The system activates the voltage acquisition module while controlling the current loop operation. This module monitors the positive and negative terminal voltages of the battery in real time according to a preset high-frequency sampling rate. The acquisition process covers the resting phase before the current pulse application, the positive charging pulse duration phase, the pulse interval phase (if any), the negative discharging pulse duration phase, and the relaxation phase after the pulse ends. The system ensures that the clock signal for voltage acquisition is highly synchronized with the clock signal for current control, so that the voltage response and current excitation can be accurately correlated on the time axis. The acquired voltage data includes not only steady-state voltage values, but more importantly, transient voltage changes during sudden current changes. These transient data are the basis for subsequent calculations of polarization amplitude and analysis of battery dynamic characteristics.

[0077] The system can achieve continuous acquisition of battery voltage at a preset sampling frequency through the following technical solutions. One solution is to use an embedded acquisition system based on a high-speed, high-precision analog-to-digital converter (ADC). The system selects a SAR (Successive Approximation Register) or Sigma-Delta ADC chip with synchronous sampling capability, and its sampling rate is set in the kHz to MHz range. The ADC front-end is equipped with a high-input-impedance instrumentation amplifier to reduce the impact of the connected circuit on the battery voltage, and is equipped with an anti-aliasing low-pass filter to filter out high-frequency noise. A microcontroller (MCU) or field-programmable gate array (FPGA) directly reads the digital quantity converted by the ADC through an SPI or I2S interface, and uses direct memory access (DMA) technology to transfer the data to the buffer at high speed, avoiding data loss due to CPU intervention. Another solution is to use a modular data acquisition card (DAQ) in conjunction with host computer software. The system connects the battery terminal voltage signal to the analog input channel of the DAQ card, which integrates signal conditioning circuitry and an ADC. The host computer communicates with the DAQ card through a USB or PCIe interface, sending sampling configuration commands (such as sampling rate, range, trigger mode, etc.). Upon receiving a trigger signal (such as a current pulse start signal), the DAQ card uses its onboard clock to perform equally spaced sampling and packages the data for upload to the host computer's memory. The host computer software utilizes multi-threading technology to receive and store the data stream, ensuring real-time performance under high data throughput.

[0078] S104. Calculate the positive polarization amplitude based on the terminal voltage; calculate the negative polarization amplitude based on the terminal voltage;

[0079] The positive polarization amplitude is calculated based on the terminal voltage. It is the absolute value of the difference between the terminal voltage at the end of the positive charging pulse and the terminal voltage at the beginning of the positive charging pulse. Similarly, the negative polarization amplitude is calculated based on the terminal voltage. It is the absolute value of the difference between the terminal voltage at the end of the negative discharging pulse and the terminal voltage at the beginning of the negative discharging pulse. The positive polarization amplitude refers to the degree to which the battery terminal voltage deviates from its equilibrium potential under the action of a positive charging pulse. Specifically, it is the difference between the voltage at the moment the charging ends and the voltage at the moment the charging begins. This difference reflects the battery's total impedance response in the charging direction, including ohmic polarization and electrochemical polarization. The negative polarization amplitude refers to the degree to which the battery terminal voltage deviates from its equilibrium potential under the action of a negative discharging pulse. It is the absolute value of the difference between the voltage at the moment the discharging ends and the voltage at the moment the discharging begins. A transient voltage sequence refers to a series of voltage data points collected at the instant of a current step change and within a very short time thereafter. The time derivative is the rate of voltage change over time, used to identify inflection points on the voltage curve. The ohmic inflection point refers to the moment when the voltage abrupt change caused by pure ohmic resistance in the voltage response ends and begins to transition to electrochemical polarization voltage change. It typically corresponds to the extreme point or step point of the voltage's differential with respect to time. The pure ohmic response voltage refers to the instantaneous voltage drop generated when current flows through the contact resistance of various components and the electrolyte resistance within the battery. The steady-state polarization voltage asymptotic value refers to the theoretical limit value at which the battery polarization voltage increases exponentially with time under continuous constant current and eventually stabilizes. The system processes the collected voltage data for both the forward charging and negative discharging processes. For the forward polarization amplitude, the system calculates the difference between the voltage at the end of the charging pulse and the voltage at the beginning; for the negative polarization amplitude, the system calculates the difference between the voltage at the end of the discharging pulse and the voltage at the beginning. To more accurately separate the polarization components, the system provides two refined calculation paths: one based on differential analysis and the other based on model fitting. Specifically, calculating the forward polarization amplitude based on the terminal voltage can be achieved using at least the following two methods:

[0080] The system can extract the transient voltage sequence within a preset time window at the instant the forward charging pulse is activated; calculate the time derivative of the transient voltage sequence and determine the ohmic inflection point when the time derivative undergoes a step change; read the inflection point voltage value corresponding to the ohmic inflection point and use it as the pure ohmic response voltage; obtain the final voltage value at the end of the forward charging pulse; and determine the absolute value of the difference between the final voltage value and the pure ohmic response voltage as the forward polarization amplitude. The system first extracts voltage data at the instant the current pulse is activated (e.g., within 0-100ms) as the transient voltage sequence. Then, the system uses a numerical differentiation algorithm (such as the five-point difference formula) to calculate the first or second derivative of this sequence. Since the ohmic voltage drop occurs instantaneously, while electrochemical polarization is gradual, a significant step or peak will appear in the derivative at the boundary between the two. The system identifies the ohmic inflection point by detecting the maximum abrupt change on the derivative curve. After determining the time, the system reads the voltage value at that time as the pure ohmic response voltage (including the initial open-circuit voltage and ohmic voltage drop). Finally, the system reads the final voltage value at the end of the pulse, subtracts the pure ohmic response voltage from it, and obtains the pure electrochemical polarization amplitude after eliminating the influence of ohmic internal resistance, or directly calculates the difference between the final voltage and the initial voltage as the total polarization amplitude.

[0081] The system can also acquire the voltage values ​​of all sampling points during the duration of the forward charging pulse to construct a charging voltage response curve; the charging voltage response curve is fitted to a preset electrochemical polarization index model using the least squares method, which includes a polarization voltage saturation term and a time constant term; the steady-state polarization voltage asymptotic value is calculated based on the fitted preset electrochemical polarization index model; the initial open-circuit voltage value at the start of the forward charging pulse is acquired; and the difference between the steady-state polarization voltage asymptotic value and the initial open-circuit voltage value is determined as the forward polarization amplitude. Specifically, calculating the steady-state polarization voltage asymptotic value based on the fitted preset electrochemical polarization index model includes the following: the functional expression of the preset electrochemical polarization index model is:

[0082] ;

[0083] in, For time Terminal voltage at time 10:00 The initial voltage, This is the pulse current value. For ohmic internal resistance, Let be the steady-state polarization amplitude parameters to be fitted. The time constant parameter to be fitted;

[0084] The charging voltage response curve is iteratively calculated using the least squares method to solve for the optimal parameters. and ;

[0085] Will and and Add them together to get The asymptotic value of the steady-state polarization voltage as it approaches infinity.

[0086] The calculation method for negative polarization amplitude is similar to that for positive polarization amplitude, and will not be repeated here.

[0087] S105. The ratio of the positive polarization amplitude to the negative polarization amplitude is used as the dynamic asymmetry coefficient;

[0088] The kinetic asymmetry coefficient is a dimensionless physical quantity used to quantify the difference in electrochemical kinetic response of a lithium-ion battery in the charging and discharging directions. This coefficient is obtained through mathematical division, with the numerator being the positive polarization amplitude and the denominator being the negative polarization amplitude. The positive polarization amplitude reflects the overall resistance during lithium-ion insertion into the negative electrode (charging), including charge transfer impedance and solid-phase diffusion impedance; the negative polarization amplitude reflects the overall resistance during lithium-ion extraction from the negative electrode (discharging). In an ideal, unaged battery without lithium plating, the kinetic characteristics of the charging and discharging processes typically exhibit a certain degree of symmetry, with the ratio approaching a specific constant. However, when abnormal reactions such as lithium plating occur inside the battery, the deposition of metallic lithium alters the reactivity and effective reaction area of ​​the electrode surface, leading to a significant change in the polarization characteristics in the charging direction, while the discharging direction is less affected, thus disrupting the original symmetry. After completing the calculation in step S103, the system calls the internal arithmetic logic unit to read the positive and negative polarization amplitude data from the memory. The system executes a division instruction to calculate the quotient of the two values. To ensure data validity, the system performs a non-zero check on the denominator (negative polarization amplitude) before calculation. The calculated quotient is the current kinetic asymmetry coefficient, which is temporarily stored in the system's data register and associated with the current timestamp, temperature, and SOC information, serving as a key indicator for subsequent assessment of battery health.

[0089] The specific calculations for this step can be implemented using the following techniques. One approach is to perform real-time floating-point operations within the microprocessor of the Battery Management System (BMS). The BMS's main control chip (such as the ARM Cortex-M series) has a floating-point unit (FPU). The system software defines two double-precision floating-point variables to store the positive and negative polarization amplitudes, respectively. During the calculation cycle, the CPU directly calls the division instruction to perform the operation and truncates and formats the result to accommodate subsequent storage or transmission protocols. If the processor does not support hardware floating-point, the system calls a fixed-point math library to amplify the voltage value by a certain factor (e.g., 1000 times) to convert it to an integer for operation, and finally restores the decimal point. Another approach is to upload the raw polarization data to a cloud server for processing. The BMS packages and sends the positive and negative polarization amplitudes to the cloud platform via a wireless communication module (such as 4G / 5G or Wi-Fi). The cloud server utilizes its powerful computing capabilities and high-level programming languages ​​(such as Python or Matlab) for data processing. The cloud platform can not only perform simple division operations, but also perform statistical analysis on historical data, calculate the moving average or standard deviation of the coefficient to eliminate random errors in single measurements, and send the calculation results back to the BMS or push them to the user terminal.

[0090] S106. Obtain the preset intrinsic symmetry reference value;

[0091] The system acquires a preset intrinsic symmetry benchmark value, which is a reference value measured under ideal experimental conditions representing the inherent kinetic symmetry characteristics of a lithium-ion battery in a healthy, lithium-free state. This benchmark value is not a single fixed constant, but a variable function closely related to the battery's current operating environment and state. Specifically, it is a function of the battery's current temperature and current state of charge (SOC). The electrochemical kinetic performance of lithium-ion batteries is greatly affected by temperature; at low temperatures, the ion diffusion rate slows down, and polarization increases. Simultaneously, the different crystal structures of electrode materials and lithium-ion concentrations at different SOCs also lead to changes in polarization characteristics. Therefore, the intrinsic symmetry benchmark value is a multi-dimensional theoretical value. Before determining lithium plating, the system must first determine this comparative "scale." The system collects real-time temperature data of the battery surface using sensors and estimates the current SOC value using the ampere-hour integration method or the open-circuit voltage method. Subsequently, the system uses these two parameters as indexes to search for or calculate the corresponding preset intrinsic symmetry benchmark value in its internally stored database or algorithm model. This benchmark value is usually obtained during the calibration phase before the battery leaves the factory. It is obtained by conducting extensive lithium-free operating condition tests (such as low-rate charge and discharge) on the same model of battery at different temperatures and SOC points, and then performing statistical analysis.

[0092] S107. If the kinetic asymmetry coefficient is determined to be greater than the preset intrinsic symmetry reference value, it is determined that lithium plating exists inside the lithium-ion battery.

[0093] Judgment refers to the process by which the system classifies the data comparison results and draws a conclusion based on logical rules. Lithium plating inside a lithium-ion battery refers to the abnormal phenomenon where, during charging, lithium ions fail to embed themselves into the graphite layered structure of the negative electrode in time, instead being reduced to metallic lithium on the surface. This usually occurs during high-rate charging, low-temperature charging, or when there is insufficient space for lithium intercalation in the negative electrode. Lithium plating not only leads to irreversible loss of battery capacity, but the generated lithium dendrites can also pierce the separator, causing internal short circuits, posing a serious safety hazard. The system compares the real-time kinetic asymmetry coefficient calculated in step S104 with the preset intrinsic symmetry benchmark value obtained in step S105. The comparison logic is based on electrochemical principles: when lithium plating occurs, the metallic lithium deposited on the negative electrode surface has extremely high reactivity, which relatively reduces the kinetic resistance of the charging process (lithium deposition) (or causes abnormal polarization voltage), while the kinetic behavior of the discharging process (lithium stripping) differs from normal lithium intercalation, causing a significant shift in the ratio between the two. Specifically, experiments show that lithium plating leads to an increase in the kinetic asymmetry coefficient, exceeding the normal range. Therefore, the system sets a judgment condition: if the measured coefficient is strictly greater than the reference value (or greater than the reference value plus a safety margin threshold), the system triggers a "lithium plating exists" judgment signal. Conversely, if the coefficient is less than or equal to the reference value, the system determines that the battery is in normal working condition and no lithium plating has occurred.

[0094] In the above embodiments, a bidirectional perturbation test current is applied to a quiescent lithium-ion battery, and the ratio of the positive and negative polarization amplitudes is calculated as the kinetic asymmetry coefficient by collecting the terminal voltage. This ratio is then compared with a preset intrinsic symmetry reference value to determine whether lithium plating exists in the battery. Since the positive charging pulse and negative discharging pulse of the bidirectional perturbation test current have equal absolute current values ​​and durations, the charging and discharging states of the battery remain dynamically balanced during the test. The kinetic asymmetry coefficient reflects the asymmetry of the positive and negative electrode kinetic responses during charging and discharging. When lithium plating occurs, the deposition of metallic lithium leads to a significant enhancement in the kinetic response during charging, while the kinetic response during discharging is relatively weak, thus increasing the kinetic asymmetry coefficient. By comparing with the preset intrinsic symmetry reference value, the kinetic asymmetry phenomenon caused by lithium plating can be effectively identified, improving the accuracy and reliability of lithium plating detection in lithium-ion batteries, reducing the interference of the current collector electronic ohmic voltage drop on the measurement data under high-rate operating conditions, and improving the accuracy of negative electrode potential monitoring, thereby improving the accuracy of determining the critical threshold for lithium plating.

[0095] The above embodiments determine whether lithium plating exists in a lithium-ion battery by using the kinetic asymmetry coefficient. To further improve the accuracy and reliability of lithium plating detection, the relaxation characteristics of the battery after the charging pulse ends can be used for verification and in-depth analysis. By observing the dynamic changes during the voltage relaxation process, two different physical processes, lithium deposition and concentration polarization, can be distinguished, thus providing a secondary confirmation of the preliminary judgment results. The following will combine... Figure 2 Another testing method for stacked three-electrode lithium-ion batteries in the embodiments of this application is described below:

[0096] Please see Figure 2 This is another flowchart illustrating a testing method for a stacked three-electrode lithium-ion battery according to an embodiment of this application.

[0097] S201. Collect the relaxation terminal voltage sequence between the end of the forward charging pulse and the preset relaxation cutoff time.

[0098] The end of the forward charging pulse refers to the instant when the charging current flowing to the positive electrode of the battery drops from a set value to zero amperes. This moment is marked by the system as the zero point of the relaxation process. The preset relaxation cutoff time refers to the moment when the system stops high-frequency data acquisition after a pre-set duration starting from the zero point. This duration is usually set according to the electrochemical characteristics of the battery and needs to be sufficient to cover the main occurrence window of the lithium plating and remelting reaction, such as a few minutes to tens of minutes. The relaxation voltage sequence refers to the set of voltage values ​​between the positive and negative electrodes of the battery continuously recorded by the system at specific sampling intervals within this time period. This sequence reflects the voltage recovery characteristics of the internal electrochemical system (including double-layer rearrangement, concentration gradient elimination, and possible side reactions such as lithium plating and remelting) as it tends towards equilibrium after the external excitation is cut off. The system immediately triggers a high-precision voltage acquisition task upon detecting the end of the forward charging pulse command. The system not only records the voltage values ​​but also accurately records the timestamp corresponding to each voltage point to ensure that subsequent time-series analysis has extremely high temporal resolution. During the data acquisition process, the system continuously monitors the battery status to ensure that the measurement is performed in an open circuit state with no current flowing through it, thus avoiding interference from load fluctuations on the pure relaxation voltage.

[0099] The system can implement this step using the following technical methods. One method is to employ Direct Memory Access (DMA) acquisition technology based on a circular buffer. The system utilizes the analog-to-digital converter (ADC) integrated within the microcontroller, configured in timer-triggered mode, to convert the battery voltage at a fixed high sampling rate (e.g., 1kHz or higher). The conversion result is directly transferred to a pre-allocated circular buffer in RAM via the DMA channel, without CPU intervention. When a charging pulse end signal is generated, the CPU locks the current buffer write pointer position as the starting point and continues to record subsequent data until a preset cutoff time is reached or the buffer is full. This method ensures that no data points are lost at the moment of current cutoff (the moment of most drastic voltage change). Another method is to use a separate high-precision data acquisition card (DAQ) in conjunction with host computer software. The system connects to the DAQ device via a high-speed bus (e.g., PCIe or USB 3.0). The host computer software issues configuration commands to set the sampling rate and trigger source (e.g., falling edge trigger). When the DAQ card detects a falling edge of the current signal, it automatically starts the onboard buffer to record the voltage waveform and uploads the data stream to the host computer's hard drive in real time. The host computer software is responsible for receiving, verifying, and storing the data in files, forming a complete time-voltage sequence file.

[0100] S202. Calculate the first-order differential sequence of the relaxation terminal voltage sequence with respect to time;

[0101] A first-order differential sequence is a set of rate values ​​of voltage change with time, i.e., a sequence of voltage derivatives with respect to time. Physically, it represents the slope of the voltage curve's tangent as it changes over time. During battery relaxation, voltage typically changes gradually over time, so the first-order differential value is usually non-zero. The purpose of calculating this sequence is to remove the DC component from the absolute voltage value, thereby highlighting the dynamic characteristics of voltage changes, especially those minute inflection points or slope changes that are difficult to detect with the naked eye on the original voltage-time curve. The system reads the relaxation voltage sequence stored in step S201 from memory. This sequence contains multiple discrete voltage points and their corresponding time points. The system uses a numerical differentiation algorithm to calculate the rate of change between adjacent or step-wise voltage points point by point. Since the original sampled data is discrete, the result calculated by the system is also a discrete time series. This process transforms the originally smooth voltage relaxation curve into a differential curve sensitive to the rate of change.

[0102] The system can implement this step using the following techniques. One method is the central difference method. For any point in the middle of the sequence, the system approximates the derivative at that point by subtracting the voltage value of the preceding point from the voltage value of the subsequent point, and then dividing by the time difference between the two points. For the first and last points of the sequence, forward and backward differences are used respectively. Compared with simple two-point difference, this method has higher truncation error accuracy and can more accurately reflect the instantaneous rate of change at that moment. Another method is to use a smoothing differential filter. The system selects a sliding window of fixed length and uses the least squares method to fit the data points into a low-order polynomial within the window. Once the coefficients of the polynomial are determined, the system directly calculates the first derivative of the polynomial at the center point as the differential value at that point. This method performs data smoothing and denoising processing simultaneously with the differential operation, and is particularly suitable for practical engineering data containing measurement noise.

[0103] S203. Determine whether there are local maxima in a first-order differential sequence;

[0104] The system determines whether a local maximum (MMR) exists in the first-order differential sequence. A MMR is an inflection point where the value of the first-order differential sequence changes from increasing to decreasing. A MMR is a point in the first-order differential sequence where the value is strictly greater than the values ​​of its two adjacent data points. Mathematically, this corresponds to a "peak" on a curve, signifying that the rate of voltage change changes from increasing to decreasing at that moment. Physically, voltage during relaxation is typically decaying, and the first-order differential value usually exhibits a specific monotonic trend. The presence of a MMR indicates an abnormal "slowdown" or even "rebound" in the rate of voltage decay within a certain time period. This is usually caused by the re-oxidation and dissolution of the lithium plating layer, generating current and thus superimposing a reverse potential change on the external terminal voltage. The system iterates through the first-order differential sequence calculated in step S202, using a comparison algorithm to find feature points that satisfy the definition of a maximum. The system not only focuses on the existence of maxima but also typically incorporates threshold judgments to eliminate small spurious peaks caused by computational noise.

[0105] S204. Confirmation of lithium plating inside the lithium-ion battery;

[0106] If a local maximum exists in the first-order differential sequence, lithium plating is confirmed to exist inside the lithium-ion battery. Lithium plating inside a lithium-ion battery refers to the phenomenon where, during charging, some lithium ions are not embedded between the graphite layers of the negative electrode but are deposited on the surface of the negative electrode as metallic lithium. This situation manifests as a specific "voltage plateau" or "rise" on the relaxation voltage curve, and directly maps to a local maximum on the first-order differential sequence. This is because the potential of metallic lithium is lower than that of lithium-intercalated graphite. When charging stops, the deposited metallic lithium will undergo oxidation with the electrolyte or the embedded negative electrode. This process establishes a mixed potential, significantly slowing down the rate of voltage decrease and even forming a peak on the differential curve. Once a valid local maximum is detected in the first-order differential sequence in step S203, the system determines that the sufficient conditions for lithium plating are met. The system then triggers its internal state machine, updating the battery's health status flag to abnormal.

[0107] S205. Since the first-order differential sequence decreases monotonically with time, calculate the first-order differential of the first-order differential sequence with respect to time to obtain the second-order differential sequence.

[0108] If there are no local maxima in the first-order differential sequence, and the first-order differential sequence is monotonically decreasing with time, the first-order differential of the first-order differential sequence with respect to time is calculated to obtain the second-order differential sequence. Monotonically decreasing means that in a mathematical sequence, the value of each subsequent element is always less than or equal to the value of the preceding element. In the context of relaxation analysis, if the first-order differential sequence is monotonically decreasing with time, it indicates that there is no inflection point that would cause an abnormal increase in the slope, and the curve is smoothly downward or tending to be stable. The second-order differential sequence refers to the second derivative of the voltage with respect to time, which is the rate of change of the first-order differential sequence with respect to time. It reflects the curvature or concavity of the voltage relaxation curve. After determining in step S203 that no local maxima were found, the system further checks the overall trend of the first-order differential sequence. If it is confirmed to be a smooth monotonic change, it indicates that there is no obvious lithium plating signal, but there may be a weak signal that is being masked. At this time, the system performs differentiation operations on the first-order differential sequence again. The calculation process is similar to that of S202, using a numerical differentiation algorithm to process the first-order differential data and generate a second-order differential data stream. The second-order differential is more sensitive to changes in the signal and can capture subtle features in the first-order differential that do not form extreme points but change in curvature.

[0109] The system can implement this step using the following techniques. One method is the cascaded differentiator method. The system reuses the differential algorithm module used in step S202. The first-order differential sequence output from step S202 is used as input data and fed back into the differential calculation function. For example, the central difference formula is applied again, and the second-order differential value is calculated by dividing the difference between the preceding and following points of the first-order differential sequence by the time interval. This method has high code reuse and is simple to implement. Another method is the direct second-order derivative extraction method based on polynomial fitting. The system performs low-order polynomial fitting on a sliding window of the original relaxation voltage sequence. After fitting, the system directly extracts the coefficients representing the second-order derivative from the polynomial coefficients obtained from the fitting. This method is mathematically more rigorous and can avoid the noise accumulation effect caused by two cascaded differentials, directly obtaining a smoother second-order differential sequence.

[0110] S206. Determine whether there are local minima in a second-order differential sequence;

[0111] The system determines whether a local minimum exists in the second-order differential sequence. A local minimum is an inflection point where the value of the second-order differential sequence changes from decreasing to increasing. A local minimum is a point in the second-order differential sequence where the value is strictly less than the values ​​of the data points on either side of it, i.e., a "valley" on the curve. Mathematically, the minimum of the second derivative corresponds to the point where the inflection point of the first derivative changes most rapidly, or to the moment when the curvature of the original voltage curve changes most drastically. Physically, when there is trace amount of lithium plating inside the battery or strong polarization masking lithium plating, although the current of lithium plating dissolution is insufficient to produce a significant bulge on the first-order differential curve, it will still change the rate of voltage recovery, causing a "step" or "shoulder" to appear on the first-order differential curve. This feature is amplified into a significant concave valley in the second-order differential sequence. The system traverses the second-order differential sequence generated in step S205, searching for the inflection point where the value changes from decreasing to increasing. The system will also apply threshold judgment logic to exclude minor fluctuations caused by calculation residuals or background noise, and only lock those minimum points whose depth exceeds a certain threshold and whose width conforms to the characteristics of electrochemical reactions.

[0112] S207. It is determined that trace amounts of lithium plating or strong polarization masking lithium plating exist inside the lithium-ion battery.

[0113] If a local minimum exists in the second-order differential sequence, it indicates that trace lithium plating or strong polarization masking lithium plating exists inside the lithium-ion battery. Trace lithium plating refers to a very small amount of deposited metallic lithium, whose mixing potential effect from dissolution is insufficient to completely reverse the voltage decay trend, only slowing down the decay rate. Strong polarization masking lithium plating refers to a situation where the battery experiences very high ohmic and concentration polarization under high-rate charging or low-temperature conditions. The rapid drop in voltage during the initial stage of voltage relaxation masks the voltage rise caused by lithium plating dissolution, making a peak invisible on the first-order differential. In both cases, the characteristics of lithium plating are "hidden." The determination refers to the system making a final diagnosis based on the search results from S206. If a definite local minimum exists in the second-order differential sequence, it indicates that although the first-order differential curve is monotonic, it has an "inflection point" or "bending change," which is strong mathematical evidence of the presence of lithium plating. Based on this, the system determines that trace lithium plating or masked lithium plating has occurred inside the battery. This step is an important supplement to the S204 determination, improving the detection sensitivity and enabling the discovery of early or hidden lithium plating phenomena.

[0114] S208, It is determined that the lithium-ion battery is in a concentration polarization-dominated state.

[0115] If no local minimum point is detected in the second-order differential sequence, the lithium-ion battery is determined to be in a concentration polarization-dominated state. A concentration polarization-dominated state refers to a state where, during the relaxation process after charging stops, the change in the battery's terminal voltage is primarily driven by the gradual elimination of the lithium-ion concentration gradient within the electrolyte and electrode materials. In this state, no side reactions such as lithium plating occur, the electrochemical system is "clean," and it conforms to the classical diffusion model. Its voltage relaxation curve should be smooth, continuous, and monotonically decaying, with the corresponding first-order differential sequence decreasing monotonically, and the second-order differential sequence also changing monotonically or remaining positive. If no local minimum point is detected in step S206, it indicates that the voltage relaxation process fully conforms to the mathematical characteristics of a pure diffusion mechanism. Based on this, the system determines that the battery is currently in a healthy concentration polarization-dominated state, and lithium plating has not occurred. This is a positive confirmation of battery safety, indicating that the current charging strategy is safe and the battery's internal kinetic balance is good.

[0116] In the above embodiments, by acquiring the relaxation voltage sequence after the positive charging pulse ends and calculating its first-order differential sequence, two different physical processes—lithium plating and concentration polarization—can be identified from the dynamic changes in the voltage relaxation process. When lithium plating is present, the dissolution process introduces additional electrochemical reactions during relaxation, resulting in a non-monotonic voltage relaxation curve, manifested as local maxima in the first-order differential sequence. In contrast, under pure concentration polarization, since only the diffusion of lithium ions in the electrolyte is involved, the voltage relaxation curve exhibits a smooth, monotonic change, with its first-order differential sequence decreasing monotonically over time. This discrimination method based on relaxation dynamics improves the accuracy of lithium plating detection and reduces the probability of misjudgment due to interference from other electrochemical processes.

[0117] The system in the embodiments of this invention is described below from the perspective of hardware processing. Please refer to [link / reference needed]. Figure 3 This is a schematic diagram of the physical device structure of a stacked three-electrode lithium-ion battery testing system provided in an embodiment of this application.

[0118] It should be noted that, Figure 3 The structure of the system shown is merely an example and should not impose any limitations on the functionality and scope of use of the embodiments of the present invention.

[0119] like Figure 3 As shown, the system includes a Central Processing Unit (CPU) 301, which can perform various appropriate actions and processes based on a program stored in Read-Only Memory (ROM) 302 or a program loaded from storage portion 308 into Random Access Memory (RAM) 303, such as executing the methods described in the above embodiments. The RAM 303 also stores various programs and data required for system operation. The CPU 301, ROM 302, and RAM 303 are interconnected via a bus 304. An Input / Output (I / O) interface 305 is also connected to the bus 304.

[0120] The following components are connected to I / O interface 305: input section 306 including a camera, infrared sensor, etc.; output section 307 including a liquid crystal display (LCD) and speakers, etc.; storage section 308 including a hard disk, etc.; and communication section 309 including a network interface card such as a LAN (Local Area Network) card and a modem, etc. Communication section 309 performs communication processing via a network such as the Internet. Drive 310 is also connected to I / O interface 305 as needed. Removable media 311, such as a disk, optical disk, magneto-optical disk, semiconductor memory, etc., are installed on drive 310 as needed so that computer programs read from them can be installed into storage section 308 as needed.

[0121] In particular, according to embodiments of the present invention, the processes described above with reference to the flowcharts can be implemented as computer software programs. For example, embodiments of the present invention include a computer program product comprising a computer program carried on a computer-readable medium, the computer program containing computer programs for performing the methods shown in the flowcharts. In such embodiments, the computer program can be downloaded and installed from a network via communication section 309, and / or installed from removable medium 311. When the computer program is executed by central processing unit (CPU) 301, it performs the various functions defined in the present invention.

[0122] It should be noted that the computer-readable medium shown in the embodiments of the present invention can be a computer-readable signal medium or a computer-readable storage medium, or any combination thereof. A computer-readable storage medium can be, for example,—but not limited to—an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any combination thereof. More specific examples of a computer-readable storage medium may include, but are not limited to: an electrical connection having one or more wires, a portable computer disk, a hard disk, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM), flash memory, optical fiber, portable compact disc read-only memory (CD-ROM), optical storage device, magnetic storage device, or any suitable combination thereof. In the present invention, a computer-readable storage medium can be any tangible medium containing or storing a program that can be used by or in conjunction with an instruction execution system, apparatus, or device. In the present invention, a computer-readable signal medium can include a data signal propagated in baseband or as part of a carrier wave, wherein a computer-readable computer program is carried. The transmitted data signal can take many forms, including but not limited to electromagnetic signals, optical signals, or any suitable combination thereof.

[0123] The flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present invention. Each block in a flowchart or block diagram may represent a module, segment, or portion of code, which contains one or more executable instructions for implementing a specified logical function. It should also be noted that in some alternative implementations, the functions indicated in the blocks may occur in a different order than those indicated in the drawings. For example, two consecutively indicated blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. It should also be noted that each block in a block diagram or flowchart, and combinations of blocks in a block diagram or flowchart, may be implemented using a dedicated hardware-based system that performs the specified function or operation, or using a combination of dedicated hardware and computer instructions.

[0124] In another aspect, the present invention also provides a computer-readable storage medium, which may be included in the system described in the above embodiments; or it may exist independently and not assembled into the system. The storage medium carries one or more computer programs that, when executed by a processor of a system, cause the system to implement the methods provided in the above embodiments.

[0125] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit it. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

[0126] As used in the above embodiments, depending on the context, the term "when..." can be interpreted as "if...", "after...", "in response to determining...", or "in response to detecting...". Similarly, depending on the context, the phrase "when determining..." or "if (the stated condition or event) is interpreted as "if determining...", "in response to determining...", "when (the stated condition or event) is detected", or "in response to detecting (the stated condition or event)".

[0127] In the above embodiments, implementation can be achieved entirely or partially through software, hardware, firmware, or any combination thereof. When implemented using software, it can be implemented entirely or partially in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the processes or functions described in the embodiments of this application are generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, the computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., coaxial cable, fiber optic, digital subscriber line) or wireless (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any available medium that a computer can access or a data storage device such as a server or data center that integrates one or more available media. The available medium can be a magnetic medium (e.g., floppy disk, hard disk, magnetic tape), an optical medium (e.g., DVD), or a semiconductor medium (e.g., solid-state drive), etc.

[0128] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. This program can be stored in a computer-readable storage medium, and when executed, it can include the processes described in the above method embodiments. The aforementioned storage medium includes various media capable of storing program code, such as ROM or random access memory (RAM), magnetic disks, or optical disks.

Claims

1. A testing method for a stacked three-electrode lithium-ion battery, characterized in that, include: The lithium-ion battery is assembled automatically, and the lower shell, negative electrode, first separator, reference electrode, second separator, positive electrode and upper shell are stacked and sealed in sequence. The assembled lithium-ion battery is transferred to a test location that integrates a temperature chamber and a charge / discharge machine for in-situ testing. When the lithium-ion battery is in a static state, a control current loop applies a bidirectional disturbance test current to the lithium-ion battery. The bidirectional disturbance test current is composed of positive charging pulses and negative discharging pulses alternating in time sequence, and the absolute value of the current of the positive charging pulse and the negative discharging pulse are equal and the duration is equal. The terminal voltage of the lithium-ion battery is continuously collected at a preset sampling frequency; The forward polarization amplitude is calculated based on the terminal voltage, where the forward polarization amplitude is the absolute value of the difference between the terminal voltage at the end of the forward charging pulse and the terminal voltage at the start of the forward charging pulse. The negative polarization amplitude is calculated based on the terminal voltage, where the negative polarization amplitude is the absolute value of the difference between the terminal voltage at the end of the negative discharge pulse and the terminal voltage at the beginning of the negative discharge pulse. The ratio of the positive polarization amplitude to the negative polarization amplitude is used as the dynamic asymmetry coefficient; Obtain a preset intrinsic symmetry reference value, wherein the preset intrinsic symmetry reference value is the theoretical value of the kinetic asymmetry coefficient of the lithium-ion battery in the non-lithium-plated state and corresponding to the current temperature and state of charge; If the dynamic asymmetry coefficient is determined to be greater than the preset intrinsic symmetry reference value, it is determined that lithium plating exists inside the lithium-ion battery; Collect the relaxation terminal voltage sequence between the end time of the forward charging pulse and the preset relaxation cutoff time; Calculate the first-order differential sequence of the relaxation terminal voltage sequence with respect to time; Determine whether there is a local maximum point in the first-order differential sequence. The local maximum point is the inflection point where the value of the first-order differential sequence changes from increasing to decreasing. If the local maximum point exists in the first-order differential sequence, then lithium plating is confirmed to exist inside the lithium-ion battery. If there is no local maximum point in the first-order differential sequence, and the first-order differential sequence decreases monotonically with time, then the lithium-ion battery is determined to be in a concentration polarization-dominated state.

2. The method according to claim 1, characterized in that, The calculation of the forward polarization amplitude based on the terminal voltage specifically includes: Extract the transient voltage sequence within a preset time window at the instant the positive charging pulse is activated; Calculate the time derivative of the transient voltage sequence and determine the ohmic inflection point when the time derivative undergoes a step change; Read the inflection point voltage value corresponding to the ohmic inflection point moment, and use the inflection point voltage value as the pure ohmic response voltage; Obtain the final voltage value at the end of the forward charging pulse; The absolute value of the difference between the final voltage value and the pure ohmic response voltage is determined as the positive polarization amplitude.

3. The method according to claim 1, characterized in that, The calculation of the forward polarization amplitude based on the terminal voltage specifically includes: The voltage values ​​of all sampling points during the duration of the forward charging pulse are obtained to construct a charging voltage response curve; The charging voltage response curve is fitted to a preset electrochemical polarization index model using the least squares method. The preset electrochemical polarization index model includes a polarization voltage saturation term and a time constant term. The asymptotic value of steady-state polarization voltage is calculated based on the fitted preset electrochemical polarization index model. Obtain the initial open-circuit voltage value at the start of the forward charging pulse; The absolute value of the difference between the steady-state polarization voltage asymptotic value and the initial open-circuit voltage value is determined as the positive polarization amplitude.

4. The method according to claim 3, characterized in that, The step of calculating the asymptotic value of the steady-state polarization voltage based on the fitted preset electrochemical polarization index model specifically includes: The functional expression of the preset electrochemical polarization index model is: ； in, For time Terminal voltage at time 10:00 The initial voltage, This is the pulse current value. For ohmic internal resistance, Let be the steady-state polarization amplitude parameters to be fitted. The time constant parameter to be fitted; The charging voltage response curve is iteratively calculated using the least squares method to obtain the optimal parameters. and stated ; The With the and Add them together to get the above. The asymptotic value of the steady-state polarization voltage as it approaches infinity.

5. The method according to claim 1, characterized in that, Before determining that the lithium-ion battery is in a concentration polarization-dominated state, the method further includes: Calculate the first-order differential of the first-order differential sequence with respect to time to obtain the second-order differential sequence; Determine whether there is a local minimum point in the second-order differential sequence. The local minimum point is the inflection point where the value of the second-order differential sequence changes from decreasing to increasing. If the local minimum point exists in the second-order differential sequence, it is determined that there is trace amount of lithium plating inside the lithium-ion battery or strong polarization masking lithium plating. If no local minimum point exists in the second-order differential sequence, the lithium-ion battery is determined to be in a concentration polarization-dominated state.

6. The method according to claim 5, characterized in that, The determination of whether a local minimum point exists in the second-order differential sequence specifically includes: Identify all candidate points of minimum value in the second-order differential sequence; Calculate the peak-valley depth corresponding to each of the minimum candidate points, where the peak-valley depth is the absolute value of the difference between the minimum candidate point and the adjacent maximum point; If the peak-valley depth of at least one candidate minimum point is greater than a preset feature significance threshold, then it is determined that the local minimum point exists in the second-order differential sequence.

7. A testing system for stacked three-electrode lithium-ion batteries, characterized in that, The system includes: One or more processors and a memory; the memory is coupled to the one or more processors, the memory being used to store computer program code, the computer program code including computer instructions, the one or more processors invoking the computer instructions to cause the system to perform the method as described in any one of claims 1-6.

8. A computer-readable storage medium comprising instructions, characterized in that, When the instructions are executed on the system, the system performs the method as described in any one of claims 1-6.

9. A computer program product, characterized in that, When the computer program product is run on the system, the system performs the method as described in any one of claims 1-6.

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