Lithium ion battery thermal runaway early warning method based on electrochemical impedance characteristics
By measuring the electrochemical impedance spectroscopy of lithium-ion batteries and extracting characteristic parameters Z″ and θ, the risk of thermal runaway of lithium-ion batteries can be monitored in real time. This solves the problems of monitoring lag and poor adaptability in existing technologies, and realizes early warning and high-reliability safety management.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-30
- Publication Date
- 2026-04-03
AI Technical Summary
Existing lithium-ion battery thermal runaway monitoring technologies are lagging, making it difficult to provide early warnings before macroscopic thermal runaway symptoms appear. Furthermore, existing impedance signal analysis methods involve large amounts of data, complex calculations, and poor adaptability, affecting the robustness and reliability of the system.
By measuring the electrochemical impedance spectroscopy of lithium-ion batteries at different temperatures, characteristic parameters Z″ and θ, which are insensitive to SOC/SOH, are extracted, their changes are monitored in real time, multiple warning levels are defined, and corresponding control measures are implemented to form an automated safety closed loop.
It enables early warning tens of seconds to minutes before thermal runaway, reducing the risk of thermal runaway propagation, simplifying hardware design, adapting to embedded BMS, improving system safety response window and reliability, and is suitable for different battery states and application scenarios.
Smart Images
Figure CN121784546A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of lithium-ion battery safety management technology, specifically to a method for early warning of thermal runaway in lithium-ion batteries based on electrochemical impedance characteristics. Background Technology
[0002] With the continuous improvement of lithium-ion battery capacity and energy density, the potential risk of thermal runaway during operation has become a key safety bottleneck restricting its further promotion in electric vehicles, energy storage power stations, and other high-energy applications. Thermal runaway can not only lead to battery damage and uncontrolled energy release, but also cause fires or explosions, posing a serious threat to safety and system reliability. Existing thermal runaway monitoring and protection technologies mainly rely on macroscopically observable signals such as surface temperature rise, flammable gas release, and voltage or current surges to identify risks. However, these methods have significant time lag: by the time temperature, gas, or voltage signals are detected, the battery has already entered a critical stage of strong self-heating or thermal runaway, leaving limited response time and failing to meet the requirements of "proactive risk perception" in high-safety application scenarios.
[0003] To achieve earlier identification of thermal risks, researchers have begun to focus on changes in microscopic signals within batteries, especially EIS characteristics. Electrochemical impedance spectroscopy (EIS) can reflect the evolution of polarization, charge transfer, and interfacial reactions within the battery, providing early warning information before macroscopic thermal runaway symptoms appear. This early warning capability provides a theoretical basis for constructing an early warning system for thermal runaway. However, existing research on impedance signal-assisted safety assessment still has two limitations: firstly, many methods rely on full-band impedance spectroscopy analysis, resulting in large amounts of data, high computational complexity, and increased difficulty in engineering deployment; secondly, the selection of impedance features lacks adaptability to different battery states (such as different SOH, SOC, and aging levels), making it difficult to reuse warning criteria, thus affecting the robustness and reliability of the system. Summary of the Invention
[0004] The purpose of this invention is to propose a method for early warning of thermal runaway in lithium-ion batteries based on electrochemical impedance characteristics. This technical solution can efficiently and lightweightly make advance judgments and actively intervene in the risk of thermal runaway in lithium batteries.
[0005] To achieve the above objectives, this invention proposes a method for early warning of thermal runaway in lithium-ion batteries based on electrochemical impedance characteristics, comprising: Electrochemical impedance spectroscopy of lithium-ion batteries at different temperatures was measured. Extract feature parameters at different frequencies, including the real part Z′, the imaginary part Z″, the magnitude |Z|, and the phase angle θ; and identify parameters and their corresponding frequencies that are insensitive to battery health and state of charge from the feature parameters. Inducing battery thermal runaway and real-time monitoring of changes in electrochemical impedance spectroscopy characteristic parameters at the insensitive frequency; Based on the combined criteria of Z″ and θ, the battery thermal runaway process is divided into multiple warning levels; Implement corresponding control measures based on different warning levels.
[0006] Beneficial effects of the basic scheme: The characteristic parameters such as Z″ and θ selected by this method can directly reflect the microscopic evolution of polarization and interface reactions such as SEI film decomposition, lithium dendrite growth, and interface impedance abrupt change inside the battery. Their abnormal changes are much earlier than traditional macroscopic signals such as temperature rise, gas release, and smoke generation. Early signs of irreversible reactions can be captured before the critical state of thermal runaway.
[0007] Compared to traditional temperature / voltage-dependent solutions, this method can identify risks before the thermal runaway chain reaction is triggered, providing a warning lead time of tens of seconds to several minutes for high-energy-density power batteries and energy storage cells. This significantly improves the system's safety response window and reliability, reducing the risk of thermal runaway propagation from the source. In scenarios prone to thermal runaway, such as fast charging and high-rate discharging, it can effectively avoid signal blind spots where surface parameters are normal but internal instability has occurred, preventing intervention failures caused by signal lag in traditional monitoring.
[0008] This method focuses only on key frequency points insensitive to SOC / SOH, rather than full-spectrum analysis, significantly reducing data acquisition volume, computational complexity, and communication load, making it suitable for the limited computing power and storage resources of embedded BMS. It eliminates the need for new complex sensing devices, allowing reuse of existing AC impedance measurement modules in the BMS, simplifying hardware design. The lightweight algorithm facilitates online deployment, reducing system hardware and software development, integration, and maintenance costs. The simplified data processing flow shortens the latency of feature extraction and early warning judgment, meeting millisecond-level online monitoring requirements and adapting to real-time safety management under dynamic operating conditions such as vehicle driving and energy storage charging / discharging.
[0009] The core characteristic parameters are insensitive to changes in battery state of charge (SOC) and state of health (SOH), maintaining consistent criteria across new batteries, aged batteries, and different charge / discharge stages, thus avoiding false alarms / missed alarms caused by state drift. It can seamlessly adapt to various application scenarios such as electric vehicles, energy storage power stations, and portable energy storage, covering different levels including single cells / modules / battery packs, while also being compatible with mainstream battery systems such as ternary lithium and lithium iron phosphate, demonstrating strong versatility.
[0010] Based on the Z″ and θ combined criteria, multiple early warning levels can be matched with tiered control measures such as "reduce power → stop charging and discharging → disconnect high voltage circuit → start forced cooling", avoiding excessive intervention or insufficient response caused by a single early warning threshold.
[0011] By linking early warning and control, an automated safety closed loop is formed. In the early stages of thermal runaway, power limiting and thermal management intervention can be used to interrupt the chain of exothermic reactions, significantly reducing the probability and scale of thermal runaway accidents. The graded early warning data can be synchronized to the cloud, providing a basis for safety status traceability and fault location for the entire battery life cycle management, assisting operation and maintenance personnel in formulating precise maintenance strategies, and improving the system's safety level.
[0012] As a feasible preferred approach, the electrochemical impedance spectroscopy measurement of the battery should be performed when the battery temperature is in a stable phase, and the battery should be tested with different states of health and different states of charge, with the states of charge covering 0%, 50%, and 100%, and the states of health covering 80%, 90%, and 100%.
[0013] As a feasible preferred approach, the electrochemical impedance spectroscopy of the battery is measured by stepwise temperature increase and simultaneous application of a small voltage perturbation, and the electrochemical impedance data of the battery at at least one fixed frequency point within a specific frequency band is obtained at each temperature rise plateau.
[0014] As a feasible preferred solution, the temperature rise step size is set to 5℃, the waiting and search time for the temperature rise platform is 60 min, and the fixed frequency is 100Hz.
[0015] As a feasible preferred option, the selected electrochemical impedance spectroscopy characteristic parameters should meet the condition of being insensitive to changes in battery state of charge and battery health.
[0016] As a feasible preferred option, Z″ in the 79–627.8 Hz frequency band and θ in the 398–627.8 Hz frequency band are determined as robust thermal runaway monitoring characteristic parameters.
[0017] As a feasible preferred solution, an external heating element heats the battery at a preset heating rate to induce its thermal runaway.
[0018] As a feasible and preferred approach, the thermal runaway process is divided into at least three warning levels: Level 1 warning: The rate of change of Z″ is greater than the first threshold and θ shows a decreasing trend; Level 2 warning: Z″ reaches the second threshold and θ is greater than the third threshold; Level 3 warning: Z″ changes from positive to negative and θ changes from positive to negative.
[0019] As a feasible preferred embodiment, the first threshold of the first-level warning is 2 mΩ / s, the second threshold is 10 mΩ, and the third threshold is 10°.
[0020] As a feasible and preferred option, the corresponding control measures for different warning levels are as follows: A Level 1 warning will reduce the charging and discharging power; a Level 2 warning will stop charging and discharging and disconnect the battery high-voltage connection; a Level 3 warning will disconnect the operating system and initiate emergency response. Attached Figure Description
[0021] Figure 1 This is a logical schematic diagram of an embodiment of the present invention.
[0022] Figure 2 This is a schematic diagram of the ARC experimental procedure in an embodiment of the present invention.
[0023] Figures 3-11 This is a graph showing the trend of impedance characteristics during the thermal runaway process of the battery described in this invention.
[0024] Figures 12-15 This is a schematic diagram of the impedance parameter extraction process for electrochemical impedance spectroscopy features in an embodiment of the present invention.
[0025] Figures 16-18 This is a diagram showing the early warning results of heating thermal runaway in an embodiment of the present invention.
[0026] Figure 19 This is a diagram of the thermal runaway early warning strategy of the present invention. Detailed Implementation
[0027] To make the technical solution and advantages of this application clearer, the technical solution of the present invention will be further described in detail below with reference to the accompanying drawings. It is understood that the specific embodiments described herein are only some embodiments of the present invention, and are only used to explain this application, not to limit it. It should be noted that the technical features or combinations of technical features described in the following embodiments should not be considered isolated; they can be combined with each other to achieve better technical effects. The same reference numerals appearing in the accompanying drawings of the following embodiments represent the same features or components, and can be applied to different embodiments.
[0028] Furthermore, unless otherwise defined, the technical or scientific terms used in this invention description shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains.
[0029] The present invention will now be described in further detail with reference to the accompanying drawings.
[0030] This disclosure provides a method for early warning of thermal runaway in lithium-ion batteries based on electrochemical impedance characteristics. The equipment involved includes a heating adiabatic calorimeter (ARC), a real-time online electrochemical impedance spectroscopy (EIS) measurement device, a heating element, and a lithium-ion battery.
[0031] The heating adiabatic calorimeter is used to simulate the thermal environment of a battery at different temperatures, and its operating mode is "heating-waiting-searching". During the waiting phase, electrochemical impedance spectroscopy measurements of the lithium-ion battery are initiated by a slight voltage perturbation to ensure that accurate impedance data is obtained when the battery is in a stable state.
[0032] The real-time online electrochemical impedance spectroscopy (EIS) measurement device includes a multi-frequency measurement module capable of simultaneously acquiring AC impedance. This module can select a single fixed frequency point within a specific frequency band for measurement. The measurement data is transmitted to the analysis unit in real time via a data acquisition system.
[0033] Heating element: Used to simulate the effect of an external heat source and induce thermal runaway in the battery.
[0034] Lithium-ion batteries: Batteries with different SOH (e.g., 100%, 90%, 80%) and different SOC (e.g., 100%, 50%, 0%) were selected for testing to cover the entire life cycle of the batteries.
[0035] Reference Figure 1 Specifically, it includes the following steps.
[0036] Step S1, linkage measuring device, including: Link the ARC with the EIS real-time online measurement device. (Refer to...) Figure 2 The ARC employs a "heating / waiting / searching" mode, with each temperature rise plateau having a waiting and search time of 60 minutes to obtain impedance data during the steady-state phase. In this embodiment, the temperature rise step size is set to 5°C.
[0037] During the waiting phase, EIS measurements of the lithium-ion battery are initiated by a slight voltage perturbation (±5 mV). The multi-frequency measurement module of the EIS measurement device selects a single fixed frequency point (e.g., 100 Hz) within a specific frequency band (e.g., 31.3–627.8 Hz) for measurement, acquiring the battery's electrochemical impedance data at that frequency point. The measurement data is transmitted to the analysis unit in real time via the data acquisition system.
[0038] The above measurements were performed on batteries with different SOH (100%, 90%, 80%) and different SOC (100%, 50%, 0%) to cover the entire battery life cycle. For example, the battery with SOH and SOC of 100% was measured first, and then the SOC was changed to 50% and 0% in turn. The above process was then repeated with batteries with SOH of 90% and 80%.
[0039] Electrochemical impedance spectroscopy (EIS) measurements of lithium-ion batteries are initiated by a slight voltage perturbation to ensure accurate impedance data is obtained under stable conditions. During this stage, the battery's EIS variation curves at different temperatures are acquired through gradual heating and continuous measurement, providing a data foundation for subsequent characteristic parameter screening and early warning classification.
[0040] Step S2: Extract and identify feature parameters, including: Reference Figure 3 Figure 11 The electrochemical impedance spectra are measured in the range of 10 kHz–0.01 Hz under different SOH and SOC conditions.
[0041] based on Figures 3 to 11 Key characteristic parameters at different frequencies were extracted from the measured electrochemical impedance spectroscopy, including the real part Z′, the imaginary part Z″, the magnitude |Z|, and the phase angle θ. The formula for calculating the magnitude |Z| is:
[0042] Analyze the characteristic evolution patterns under different SOC and SOH conditions, such as plotting curves of the real part Z′, imaginary part Z″, modulus |Z|, and phase angle θ as a function of SOC and SOH. By observing the curves, identify parameters that are insensitive to changes in battery state and their corresponding frequencies. This allows for the determination of reusable and robust thermal runaway monitoring characteristics, ensuring the reliability of the early warning criteria throughout the battery's entire lifespan and under different operating conditions.
[0043] Reference Figures 12 to 15 The distribution of four characteristic parameters with varying SOC and SOH is shown to illustrate their differences in sensitivity. Z′ is mainly distributed in the range of 0.04–0.05 at 50% and 0% SOC, shifting upward to 0.06–0.07 at 100% SOC; it remains at 0.03–0.04 under fresh and 80% SOH conditions, while increasing to 0.06–0.07 at 90% SOH. |Z| shows the same behavior as Z′, ranging from 0.04–0.06 at 50% and 0% SOC, shifting upward to 0.065–0.075 at 100% SOC; it is 0.03–0.06 under fresh and 80% SOH conditions, while increasing to 0.07–0.08 at 90% SOH.
[0044] Refer to 12 to Figure 15Furthermore, it can be seen that Z″ is insensitive to changes in SOC within the frequency range of 31.3–627.8 Hz and insensitive to changes in SOH within the range of 79–796.9 Hz. Therefore, Z″ can be considered to be insensitive to both SOC and SOH simultaneously within the 79–627.8 Hz range. The curves of θ for SOC changes largely overlap within the 398–796.9 Hz range and also overlap for SOH within the 315.5–627.8 Hz range, exhibiting insensitive characteristics to both SOC and SOH within the 398–627.8 Hz range.
[0045] Z″ in the 79–627.8 Hz band and θ in the 398–627.8 Hz band were identified as reusable and robust thermal runaway monitoring characteristic parameters.
[0046] Step S3, inducing and monitoring thermal runaway, includes: A heating element is used to simulate an external heat source, and it is tightly attached to the battery surface. The battery is heated at a certain rate (e.g., 5°C / min) to induce thermal runaway.
[0047] During the heating process, the changes in Z″ at insensitive frequencies (79–627.8 Hz) and θ at low-sensitivity frequencies (398–627.8 Hz) are monitored in real time. By observing the changing trends of characteristic parameters under thermal runaway, the early evolution of internal polarization and interfacial reactions of the battery can be captured, thereby identifying potential thermal risks in advance and providing a basis for graded early warning.
[0048] Step S4: Based on the feature combination criteria, the battery thermal runaway process is divided into multiple warning levels.
[0049] The warning level can be defined based on the rate of change, amplitude, and trend of characteristic parameters of battery thermal runaway, so as to achieve a quantitative description of the risk of thermal runaway.
[0050] Reference Figures 16 to 18 The figure shows the relationship between impedance characteristics and temperature rise. Under external heating conditions, when Z″ is close to 10 mΩ, the temperatures are 45.1℃, 49.56℃, and 68.27℃, respectively; when θ>10°, the temperatures are 55.99℃, 65.12℃, and 64.11℃, respectively. Figure 5 As shown, when the natural temperature rise continues beyond the peak range of self-heating, Z″ changes from positive to negative within the range of approximately 105–120℃. Further temperature increases, such as... Figure 5 As shown, within the range of 130–145℃, θ changes from positive to negative, corresponding to the critical stage of thermal runaway triggering.
[0051] Three or more levels of early warning can be set, corresponding to abnormal temperature rise, obvious self-heating and critical thermal runaway state, respectively, to ensure that there is a targeted risk assessment at each stage.
[0052] Reference Figure 19 Taking the setting of a three-level early warning system as an example: Level 1 Warning: When the rate of change of Z″ exceeds a set threshold (e.g., the change of Z″ per unit time is greater than 2 mΩ / s) and θ begins to show a significant decreasing trend (e.g., the decrease in θ exceeds 3°), it is judged as a Level 1 warning, corresponding to an abnormal temperature rise state. At this time, slight polarization changes may begin to occur inside the battery, but it has not yet entered a significant self-heating stage; Level 2 warning: When Z″ approaches 10 mΩ (the specific value can be adjusted according to actual experimental data) and θ>10°, it is judged as a Level 2 warning, corresponding to a significant self-heating state. At this time, the chemical reaction inside the battery intensifies, the self-heating phenomenon is obvious, and the risk of thermal runaway further increases; Level 3 warning: When Z″ changes from positive to negative (within the range of approximately 105–120℃) and θ changes from positive to negative (within the range of 130–145℃), a Level 3 warning is issued, corresponding to the critical state of thermal runaway. At this point, the battery is in an extremely unstable state and thermal runaway is about to occur.
[0053] Step S5 involves implementing corresponding control measures based on different warning levels, including but not limited to disconnecting external circuits, activating the forced cooling system, reducing the charge / discharge rate, or triggering safety protection devices, to achieve early intervention and proactive control of thermal runaway. Through the linkage between the graded judgment module and the control execution module, an automated closed-loop control can be formed, enabling dynamic safety management of high-energy lithium-ion batteries under complex operating conditions and improving the overall safety and reliability of the system.
[0054] In this embodiment, the specific details are as follows: During a Level 1 warning: The system reduces the charging and discharging power. A command is sent through the Battery Management System (BMS) to reduce the battery's charging and discharging power to 50% of its rated power, thereby slowing down the rate of internal chemical reactions and reducing the risk of thermal runaway.
[0055] During a Level 2 warning: charging and discharging are stopped and the battery high-voltage connection is disconnected. The BMS sends a command to disconnect the charging and discharging circuit between the battery and the external circuit, and simultaneously disconnects the battery's high-voltage connection to prevent further energy release and the further development of thermal runaway.
[0056] During a Level 3 warning: The operating system is shut down and emergency response is initiated. The BMS sends an emergency shutdown signal to cut off the operation of the entire electric vehicle or energy storage system, and simultaneously activates emergency response procedures, such as triggering fire extinguishing devices and ventilation systems, to minimize the losses caused by thermal runaway.
[0057] The feature determination lead time is in the range of 193–593 s, which can provide intervention time before thermal runaway occurs.
[0058] The control execution module and the grading judgment module are linked. The grading judgment module analyzes the monitored electrochemical impedance spectroscopy characteristic parameters in real time, makes a judgment based on preset warning level judgment conditions, and sends the judgment result to the control execution module. Based on the received judgment result, the control execution module immediately executes corresponding control measures, forming an automated closed-loop control. For example, when the grading judgment module determines a level one warning, the control execution module automatically reduces the charging and discharging power without manual intervention, thereby improving the system's response speed and safety.
[0059] The above content is merely an embodiment of the present invention. Commonly known structures and characteristics of the solutions are not described in detail here. Those skilled in the art are aware of all common technical knowledge in the field prior to the application date or priority date, are aware of all existing technologies in that field, and have the ability to apply conventional experimental methods prior to that date. Those skilled in the art can improve and implement this solution based on the guidance provided in this application and their own capabilities. Some typical known structures or methods should not be obstacles for those skilled in the art to implement this application. It should be noted that those skilled in the art can make several modifications and improvements without departing from the structure of the present invention. These should also be considered within the scope of protection of the present invention, and will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.
Claims
1. A method for early warning of thermal runaway in lithium-ion batteries based on electrochemical impedance characteristics, characterized in that, include: Electrochemical impedance spectroscopy of lithium-ion batteries at different temperatures was measured; Extract feature parameters at different frequencies, including the real part Z′, the imaginary part Z″, the magnitude |Z|, and the phase angle θ; and identify parameters and their corresponding frequencies that are insensitive to battery health and state of charge from the feature parameters. Inducing battery thermal runaway and real-time monitoring of changes in electrochemical impedance spectroscopy characteristic parameters at the insensitive frequency; Based on the combined criteria of Z″ and θ, the battery thermal runaway process is divided into multiple warning levels; Implement corresponding control measures based on different warning levels.
2. The method for early warning of thermal runaway in lithium-ion batteries based on electrochemical impedance characteristics according to claim 1, characterized in that, Electrochemical impedance spectroscopy measurements of the battery must be performed when the battery temperature is stable, and batteries with different states of health and different states of charge must be tested, with the states of charge covering 0%, 50%, and 100%, and the states of health covering 80%, 90%, and 100%.
3. The method for early warning of thermal runaway in lithium-ion batteries based on electrochemical impedance characteristics according to claim 2, characterized in that, The electrochemical impedance spectroscopy of the battery is measured by stepwise heating and simultaneous application of a small voltage perturbation. At each temperature rise plateau, the electrochemical impedance data of the battery at at least one fixed frequency point within a specific frequency band is obtained.
4. A method for early warning of thermal runaway in lithium-ion batteries based on electrochemical impedance characteristics according to claim 1, characterized in that, The temperature rise step size was set to 5℃, the waiting and search time for the temperature rise platform was 60 min, and the fixed frequency was 100Hz.
5. The method for early warning of thermal runaway in lithium-ion batteries based on electrochemical impedance characteristics according to claim 1, characterized in that, The selected electrochemical impedance spectroscopy characteristic parameters should meet the condition of being insensitive to changes in the battery's state of charge and state of health.
6. A method for early warning of thermal runaway in lithium-ion batteries based on electrochemical impedance characteristics according to claim 1, characterized in that, Z″ in the 79–627.8 Hz frequency band and θ in the 398–627.8 Hz frequency band were determined as robust thermal runaway monitoring characteristic parameters.
7. The method for early warning of thermal runaway in lithium-ion batteries based on electrochemical impedance characteristics according to claim 1, characterized in that, An external heating element heats the battery at a preset heating rate to induce thermal runaway.
8. The method for early warning of thermal runaway in lithium-ion batteries based on electrochemical impedance characteristics according to claim 1, characterized in that, The thermal runaway process is divided into at least three warning levels: Level 1 warning: The rate of change of Z″ is greater than the first threshold and θ shows a decreasing trend; Level 2 warning: Z″ reaches the second threshold and θ is greater than the third threshold; Level 3 warning: Z″ changes from positive to negative and θ changes from positive to negative.
9. A method for early warning of thermal runaway in lithium-ion batteries based on electrochemical impedance characteristics according to claim 8, characterized in that, The first threshold for the Level 1 warning is 2 mΩ / s, the second threshold is 10 mΩ, and the third threshold is 10°.
10. A method for early warning of thermal runaway in lithium-ion batteries based on electrochemical impedance characteristics according to claim 8 or 9, characterized in that, The corresponding control measures for different warning levels are as follows: A Level 1 warning will reduce the charging and discharging power; a Level 2 warning will stop charging and discharging and disconnect the battery high-voltage connection; a Level 3 warning will disconnect the operating system and initiate emergency response.