In-situ monitoring device for internal state of lithium battery

Abstract

This invention belongs to the field of lithium battery anomaly detection technology and discloses an in-situ monitoring device for the internal state of a lithium battery. The device includes a fiber optic grating sensing probe, which is inserted into the central axial cavity of a cylindrical lithium battery. One end of the probe passes through the battery top cover and connects to a signal demodulation unit, while the other end is suspended within the cavity. The probe includes an optical fiber with a grating etched on it at a 45° angle to its cross-section, enabling the separation of the optical signal into a radiation mode intensity signal and a core mode intensity signal. The signal demodulation unit is configured to simultaneously acquire the radiation mode intensity signal and the core mode intensity signal, perform a ratio calculation, and obtain a real-time discrimination coefficient. Based on the changing trend of the discrimination coefficient, the presence of an anomaly is determined. This invention can distinguish between changes in the internal liquid phase environment and anomalies in the solid phase structure of the battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery anomaly detection technology, and particularly relates to an in-situ monitoring device for the internal state of a lithium battery. Background Technology

[0002] Existing research primarily employs fiber Bragg gratings, long-period gratings, or corrosion-prone fiber optic sensors to monitor parameters such as internal temperature, strain, or electrolyte refractive index of lithium-ion batteries in real time, indirectly reflecting the battery's operating status. Cylindrical lithium-ion batteries, due to their wound electrode structure, are susceptible to non-uniform lithium deposition and interfacial microstructure evolution on the innermost negative electrode surface, leading to solid-phase anomalies. These anomalies often coexist with changes in the liquid phase environment, such as electrolyte concentration polarization and temperature fluctuations, and their effects on fiber optic sensing signals are highly additive and cross-sensitive. Traditional fiber optic sensors struggle to distinguish the signal response differences caused by changes in the internal liquid phase environment and solid-phase structure evolution of cylindrical lithium-ion batteries, resulting in low accuracy in identifying solid-phase anomalies. Summary of the Invention

[0003] To overcome the shortcomings of the prior art, the present invention provides an in-situ monitoring device for the internal state of a lithium battery, which can distinguish between anomalies caused by changes in the liquid phase environment and the evolution of the solid phase structure, thereby improving the accuracy of anomaly identification.

[0004] To achieve the above objectives, one or more embodiments of the present invention provide an in-situ monitoring device for the internal state of a lithium battery, comprising a fiber optic grating sensing probe. The probe is inserted into the central axial cavity of a cylindrical lithium battery, with one end passing through the battery top cover and connected to a signal demodulation unit, and the other end suspended within the cavity. The probe includes an optical fiber, on which a grating is etched at a 45° angle to the cross-section of the optical fiber, capable of separating the optical signal into a radiation mode intensity signal and a core mode intensity signal. The signal demodulation unit is configured to: synchronously acquire the radiation mode intensity signal and the core mode intensity signal, perform a ratio calculation to obtain a real-time discrimination coefficient; and determine whether an anomaly exists based on the changing trend of the discrimination coefficient.

[0005] In some embodiments, the battery top cover has holes for probes to pass through and sealing components.

[0006] In some embodiments, the end of the optical fiber suspended in the cavity is provided with a spherical end cap.

[0007] In some embodiments, the distal spherical cap surface of the spherical end cap is coated with a metal reflective film.

[0008] In some embodiments, determining whether there is a potential anomaly based on the changing trend of the discrimination coefficient includes: continuously monitoring the difference between the real-time value of the discrimination coefficient and the value at the previous moment; if the absolute value of the difference is greater than a preset step threshold and the difference remains for more than a set time, it is determined that there is a potential anomaly.

[0009] In some embodiments, the step threshold is determined as follows: under the battery health condition, the radiation mode intensity signal and the fiber core mode intensity signal are collected simultaneously, and the corresponding discrimination coefficients are calculated; the step threshold is determined based on the mean and variance of the discrimination coefficients.

[0010] In some embodiments, when a potential anomaly is detected, a charge / discharge pause command is sent to the battery management system, the discrimination coefficient is continuously recorded within a set time window, and the recovery rate of the discrimination coefficient within the time window is calculated; if the recovery rate is higher than a set judgment threshold, the abnormal event is determined to be caused by a change in the liquid phase environment; otherwise, the abnormal event is determined to be caused by an abnormality in the solid phase structure.

[0011] In some embodiments, the determination of the judgment threshold is as follows: under the battery health state, the radiation mode intensity signal and the core mode intensity signal are collected simultaneously, and the real-time discrimination coefficient is calculated; when the judgment coefficient exceeds the step threshold, a charge / discharge pause command is sent to the battery management system, the discrimination coefficient is continuously recorded within a set time window, and the recovery rate of the discrimination coefficient within the time window is calculated; the judgment threshold is determined based on the mean and variance of the recovery rate.

[0012] In some embodiments, if the abnormal event is caused by a change in the liquid phase environment, the charging current rate is reduced after the battery resumes operation; if the abnormal event is caused by an abnormal solid phase structure, if the recovery rate does not reach the critical threshold, the power-off resting time is extended, and operation is resumed after the discrimination coefficient stabilizes; if the recovery rate reaches the critical threshold, the power-off state is maintained.

[0013] In some embodiments, the method further includes: acquiring historical solid-phase abnormal events, and providing graded early warning of battery health status based on the changing trends of at least two of the cumulative occurrence frequency, discrimination coefficient offset, and event duration.

[0014] The above one or more technical solutions are based on the solid-phase abnormal growth characteristics of the cylindrical lithium battery winding structure and the difference in probe deformation recovery law caused by liquid-phase abnormalities and solid-phase abnormalities. By setting up an optical fiber probe structure with a 45° tilted grating, temperature interference and abnormal signals are decoupled. Then, based on the response difference of the two decoupled signals, the difference between changes in the liquid-phase environment inside the battery and solid-phase structural abnormalities can be distinguished. Attached Figure Description

[0015] The dimensions and scales in the accompanying drawings do not represent the actual dimensions and scales of the product. The drawings are for illustrative purposes only, and some non-essential elements or features have been omitted for clarity.

[0016] Figure 1 This is a schematic diagram of an in-situ monitoring device for the internal state of a lithium battery provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the deformation of the in-situ monitoring device provided in an embodiment of the present invention under a state of abnormal solid-phase contact. Figure 3 This is a schematic diagram of the process for identifying internal abnormal states of a lithium battery based on the discriminant coefficient and recovery rate, provided in an embodiment of the present invention.

[0017] Illustration: 1. Sealing assembly, 2. Fiber core, 3. Cladding, 4. Grating, 5. Spherical end cap, 6. Cylindrical cell, 7. Solid-phase anomalous structure. Detailed Implementation

[0018] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0019] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0020] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0021] In this invention, terms such as "upper," "lower," "side," and "bottom" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are merely relational terms determined for the convenience of describing the structural relationship of the various components or elements of this invention, and do not specifically refer to any component or element in this invention, and should not be construed as limiting this invention.

[0022] In this invention, terms such as "connection" should be interpreted broadly, indicating a fixed connection, an integral connection, or a detachable connection; it can be a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can determine the specific meaning of the above terms in this invention based on the specific circumstances, and they should not be construed as limitations on this invention.

[0023] Where there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0024] Cylindrical lithium-ion battery cells are formed by winding positive and negative electrode sheets and a separator, naturally creating a through-cylindrical cavity along their central axis. This cavity is connected to the electrolyte environment inside the cell, and its size is well-suited to the size of fiber optic sensors, making it a suitable carrier for in-situ detection fiber optic sensors with spatial feasibility. Currently, the mainstream in-situ detection solutions use fiber Bragg grating (FBG) sensors and Fabry-Perot (FP) fiber optic sensors. These are achieved by simultaneously winding the fiber optic sensor, equipped with an electrolyte-resistant protective sleeve, along the central axis during the cell winding stage, or by implanting the fiber optic sensor into the central cavity through a pre-drilled hole or injection hole in the cell cover, followed by sealing the exit point.

[0025] However, existing fiber optic sensors such as FBG and FP primarily respond to physical quantities like temperature and macroscopic strain in their detection signals. Different anomalies within the battery cell, such as electrolyte concentration polarization, abnormal solid-phase structures of the positive and negative electrodes (e.g., particle cracking, SEI film damage), and volume expansion stress changes during charging and discharging, can all cause shifts in the sensor's detection signal. Furthermore, the signal characteristics corresponding to different anomaly types overlap, and existing detection systems lack effective signal separation and identification mechanisms. This makes it impossible to accurately pinpoint the anomaly type based on changes in the detection signal, easily leading to misjudgments and affecting the accuracy of in-situ diagnosis. In addition, the concentration distribution and flow state of the electrolyte during charging and discharging generate dynamic interference, causing fluctuations in the sensor's detection signal and affecting the stability of parameter measurements. Moreover, the periodic volume expansion and contraction during charging and discharging of the battery cell directly affects the fiber optic sensor, triggering additional strain signals that couple with signals generated by anomalies within the battery cell, further interfering with detection accuracy.

[0026] This embodiment provides a cantilever tilted fiber optic grating sensor and monitoring method for in-situ monitoring of multiple internal abnormal states in cylindrical batteries. By using a cantilever beam fiber structure with a spherical end cap, it can perceive and distinguish various internal abnormal behaviors generated during battery operation in real time. This solves the problems of insufficient sensitivity, severe signal cross-sensitivity, and high false alarm rate caused by difficulty in distinguishing between solid phase contact and liquid phase environment changes in existing lithium battery monitoring technologies, thereby improving the safety and reliability of lithium battery operation.

[0027] Figure 1A schematic diagram of an in-situ monitoring device for the internal state of a lithium battery provided in an embodiment of the present invention is shown. The monitoring device includes a fiber optic grating sensing probe, which is inserted into the central axial cavity of a cylindrical lithium battery. One end of the probe passes through the top cover of the battery and is connected to the signal demodulation unit, while the other end is suspended in the cavity. The probe includes an optical fiber, on which a grating 4 is etched at a 45° angle to the cross-section of the optical fiber.

[0028] Unlike ordinary long-period gratings or Bragg gratings, when the grating tilt angle is 45°, the tilted grating 4 exhibits polarization-dependent coupling characteristics for light of different polarization states in the optical fiber, which can couple the transmitted optical energy to different modes. Specifically, the S-polarization component, with the electric field vector perpendicular to the incident plane, is easily coupled by the grating 4 into cladding and radiation modes. Its energy enters the cladding 3 and is transmitted at the interface between the outer surface of the cladding 3 and the electrolyte. Therefore, the S-polarization component is extremely sensitive to changes in the refractive index of the cladding 3, external stress, and fiber bending disturbances. In contrast, the P-polarization component, with the electric field vector parallel to the incident plane, has extremely low coupling efficiency. Its energy is mainly confined within the fiber core as a core mode and is insensitive to changes in the refractive index of the external environment, only affected by the thermo-optical effect of the fiber material caused by temperature. Utilizing the above polarization-dependent mode separation characteristics, a sensing channel (S-polarization channel) sensitive to the external environment and a reference channel (P-polarization channel) responding only to temperature are simultaneously constructed on a single optical fiber, providing a basis for signal decoupling and anti-interference detection.

[0029] During battery operation, when different types of anomalies occur inside, such as temperature disturbances, electrolyte concentration polarization, abnormal electrode solid structure, and macroscopic stress / volume expansion, the signal demodulation unit compares and analyzes the signal change characteristics of the S-polarization sensing channel and the P-polarization reference channel to eliminate temperature disturbances and distinguish different types of anomalies, thus completing in-situ real-time monitoring of the internal state of the cylindrical battery.

[0030] In some embodiments, the optical fiber is specifically a single-mode optical fiber, a tilted fiber grating region inscribed within the fiber core 2, and a spherical end cap 5 located at the free end. The single-mode optical fiber serves as the transmission medium for optical signals, and its cladding 3 typically has a diameter of 125 micrometers. The length of the probe's suspended section is designed based on the depth of the axial cavity at the center of the battery, so that its free end is suspended within the axial cavity and adjacent to the innermost negative electrode surface of the wound cell. This allows the probe to sensitively respond to the radial perturbation forces generated by the solid-phase anomalous structure growing from the innermost negative electrode surface into the central cavity.

[0031] The battery top cover has holes for the probe to pass through, and a sealed connection between the fiber optic probe and the internal environment of the battery can be achieved through the sealing assembly 1. The sealing assembly 1 is located at the center of the lithium battery top cover. During the encapsulation process, the upper end of the probe is encapsulated and fixed to the sealing assembly 1 using a sealant resistant to electrolyte corrosion. The sealant can be a modified epoxy resin sealant or a Teflon-based sealant. These materials not only provide stable mechanical fixation to prevent the probe from shifting during battery operation or vibration, but also effectively prevent electrolyte from seeping outward and prevent the internal components of the battery from reacting with the external environment.

[0032] In some embodiments, the optical fiber constituting the probe is specifically a single-mode optical fiber with a spherical end cap 5 at its free end, which does not contact the battery bottom cover. The single-mode optical fiber serves as the transmission medium for optical signals, and its cladding 3 typically has a diameter of 125 micrometers. This size is an industry standard and is much smaller than the diameter of the central axial cavity of the cylindrical battery, providing good spatial adaptability. The length of the probe's suspended section is designed according to the depth of the central axial cavity of the battery, ensuring that its free end is suspended within the central axial cavity and adjacent to the innermost negative electrode surface of the wound cell without contacting it. This avoids short circuits or mechanical damage caused by contact between the probe and the negative electrode, while also allowing the probe to sensitively respond to the radial micro-perturbation forces generated by the solid-phase anomalous structure growing from the innermost negative electrode surface into the central cavity. Figure 2 As shown, this further improves the detection sensitivity of solid-phase anomalous structures.

[0033] The distal spherical cap 5 has a metal reflective film coated on its spherical surface. The spherical cap 5 is formed by the integrated electrofusion splicing of the free end of a single-mode optical fiber using a fiber optic fusion splicer. Its diameter is approximately 130 to 160 micrometers, slightly larger than the diameter of the fiber cladding 3. This size range ensures both the inertial mass and reflective effect of the cap, while preventing excessive size from interfering with the flow of electrolyte and normal operation of the battery cell. The distal spherical surface of the spherical cap 5 is coated with a metal reflective film using a magnetron sputtering process; the material of this metal reflective film can be gold or silver. The spherical cap 5 possesses both optical reflection and mechanical enhancement functions. On one hand, the spherical cap 5 utilizes its spherical structure to converge and reflect the light beam excited by the tilted fiber grating, allowing the optical signal to return along its original path, realizing a single-end reflective measurement structure and simplifying the sensor's placement within the battery. On the other hand, the spherical cap 5, as an inertial mass element and anti-piercing protection structure at the end of a cantilever beam, is crucial for maintaining the probe's monitoring stability under complex stress. When a solid-phase anomalous structure grows on the innermost negative electrode surface and extends towards the center, the spherical end cap 5 plays a crucial role regardless of whether the solid-phase structure contacts the probe's rod sidewall or the end ball. If the solid-phase structure compresses the rod sidewall, the spherical end cap 5 utilizes its own inertia and gravity to provide stable axial tension for the suspended fiber probe, suppressing nonlinear twisting or local buckling of the fiber and ensuring that the cantilever beam produces demodulated regular bending deformation. If the solid-phase structure directly compresses the end, the spherical end cap 5 acts as a passivation probe to prevent the tip from piercing the cell and efficiently converts radial compression into bending torque. Therefore, this structure significantly improves the sensor's response sensitivity and signal reliability to solid-phase anomalous growth throughout the entire central cavity.

[0034] The surface of the cantilevered tilted fiber Bragg grating sensing probe can also be modified with a functional material layer, such as polydopamine or a specific polymer coating, to improve the probe's adsorption of specific electrolyte components or enhance its durability in highly corrosive electrolytes.

[0035] The signal demodulation unit is configured to receive the Bragg diffraction light signal reflected back by the probe, perform filtering, amplification, wavelength calibration, spectral peak tracking, phase demodulation and noise suppression processing on the light signal, and convert the changes in the light signal into corresponding wavelength drift, light intensity change and bending deformation information, thereby calculating the internal pressure of the cell, radial extrusion pressure, solid phase structure growth degree and position information, and outputting it to the host computer or data processing terminal.

[0036] When the battery is in normal condition or only the liquid phase environment changes, the probe's free-suspension section is completely immersed in the electrolyte and is only affected by electrolyte flow and viscous resistance. The force is uniform, and its deformation can be quickly restored through elastic recovery and electrolyte diffusion after the charging and discharging is stopped. The essence of this type of liquid phase anomaly is the change in ion concentration gradient. After the electrochemical reaction stops, ion diffusion will quickly eliminate the concentration gradient, allowing the electrolyte parameters to return to equilibrium. When a solid phase anomaly structure forms inside the battery and comes into contact with the probe, the probe will be subjected to lateral extrusion force. The spherical end cap 5 at the end provides axial tension through gravity and inertia, causing the probe to produce significant and regular asymmetric bending deformation. This deformation will preferentially modulate the coupling efficiency and transmission loss of the radiation mode polarization component, causing a significant change in the radiation mode intensity signal Is(t) in the reflection spectrum relative to the core mode intensity signal Ip(t). Due to the physical limitations of the solid phase structure, this deformation cannot be quickly restored after the electrochemical reaction stops. The essence of this type of solid phase anomaly is the permanent / semi-permanent deformation of the physical structure.

[0037] Based on the above principles, in some embodiments, by collecting optical signals and analyzing their characteristics, the charging and discharging of the battery is actively paused to observe the signal recovery. Based on the difference that probe deformation caused by liquid phase abnormalities can be quickly restored while deformation caused by solid phase abnormalities is hindered from recovering, a reasonable judgment threshold can be set. By comparing the recovery rate calculated in real time with the preset threshold, the identification of different types of abnormalities inside the battery can be realized.

[0038] Specifically, such as Figure 3 As shown, the method includes the following steps: S1. During battery charging and discharging, broadband light is input to the probe. Utilizing the polarization-dependent coupling characteristics of the 45° tilted fiber grating in the probe, the optical signal is separated into a radiation mode polarization component formed by S-polarization coupling and a core mode polarization component dominated by P-polarization. The two optical signals are reflected back to the signal demodulation unit through the spherical end cap 5 at the end of the probe. The signal demodulation unit synchronously acquires the radiation mode intensity signal Is(t) and the core mode intensity signal Ip(t) from the reflection spectrum. S2. Calculate the ratio between the radiation mode intensity signal and the core mode intensity signal in real time, denoted as the discrimination coefficient K(t): .

[0039] In actual operation, the battery may be affected by mechanical vibration, causing macroscopic bending of the optical fiber leads and resulting in light intensity loss. However, this loss is global for both S-mode and P-mode, meaning both will weaken simultaneously. Therefore, their ratio K(t) will remain near a relatively constant, i.e., a baseline value. Conversely, when abnormal deposition, growth, or contact behavior occurs inside the battery, or when there are drastic changes in the local electrolyte environment, these changes mainly affect the S-mode radiation, which is sensitive to the external environment, while having minimal impact on the P-mode within fiber core 2. This leads to a significant change in the discrimination coefficient K(t), based on which the system identifies potential abnormal events, i.e., executes step S3.

[0040] S3. Based on the changing trend of the discriminant coefficients, determine whether there is a potential anomaly. Specifically, if Is(t) and Ip(t) fluctuate proportionally, causing K(t) to remain stable, it is determined to be environmental interference such as mechanical vibration, and subsequent operations are not triggered. If K(t) undergoes a significant step change, it is determined that there is a potential abnormal event inside the battery. Specifically, continuously monitor the difference between the real-time value of the discriminant coefficient and the value at the previous moment. If the absolute value of the difference is greater than a preset step threshold, and the difference remains for more than a set time, a potential anomaly is determined. The preset step threshold can be the average value of the discriminant coefficients calibrated under the initial healthy state of the battery.

[0041] During high-rate charging, the rapid consumption of lithium ions on the innermost negative electrode surface of the wound cell causes a sharp drop in local refractive index, which in turn leads to the attenuation of the Is(t) signal. This behavior closely resembles solid-phase structure formation, abnormal deposition, or interface contact, making it difficult to distinguish the source of the anomaly solely based on changes in the K(t) amplitude. Therefore, based on the assessment of a potential abnormal event, an active dynamic response test is introduced. The system instructs the battery management system to temporarily cut off the charging and discharging current, causing a relaxation process within the battery, i.e., executing step S4.

[0042] S4. When a potential anomaly is detected, a command is sent to the battery management system to suspend battery charging or discharging operations and lock the power outage time. Within a set time window Δt, the values ​​of the discrimination coefficient K(t) are continuously recorded, and the recovery slope of K(t) within this time interval is calculated as the recovery rate. The formula for calculating the recovery rate is:

[0043] The choice of the time window Δt depends on the diffusion coefficient D of the electrolyte and the characteristic size of the probe. Typically, the diffusion coefficient of lithium ions in the electrolyte is around 10⁻⁶ cm⁻¹. 2The relaxation time of the concentration field is typically on the order of seconds (in the order of seconds). Therefore, setting Δt between 0.1 and 5 seconds is reasonable, as it captures the diffusion process without being too long and affecting the battery's efficiency.

[0044] S5. Calculate the recovery rate. Compared with the preset judgment threshold Comparison: If Higher than The abnormal event was determined to be caused by a change in the liquid phase environment; if Below The abnormal event was determined to be caused by an anomaly in the solid phase structure.

[0045] It is understood that the above scheme will only trigger a brief pause in charging and discharging to conduct relaxation testing when a potential abnormal event is detected. The time window for relaxation testing is a brief pause in the millisecond to second range, which is much shorter than the battery charge and discharge cycle and will not affect the battery's charge and discharge efficiency, capacity decay, or lifespan. Furthermore, charging and discharging can be quickly resumed after the pause based on the abnormality detection result, enabling real-time and reliable monitoring throughout the battery's lifespan while taking into account both monitoring accuracy and the normal use requirements of the battery.

[0046] Based on the differences in the physical relaxation laws of liquid-phase and solid-phase anomalies, an active dynamic recovery characteristic test is introduced. Combined with the judgment threshold, this effectively solves the problem of signal feature confusion between liquid-phase concentration polarization and solid-phase anomalies under high-rate charging, and enables the differentiation between the two types of anomalies.

[0047] The above anomaly determination results can serve as the basis for triggering safety warnings or battery protection strategies. Specifically, for anomalies dominated by changes in the liquid phase environment, the charging current rate should be appropriately reduced after operation resumes to alleviate concentration polarization. Regarding the recovery rate... Below the judgment threshold However, since the critical threshold for danger has not yet been reached, a control strategy of extending the power outage settling time is implemented, and the restricted operation mode is allowed after the signal characteristics are detected to have stabilized; regarding the recovery rate... Significantly below the judgment threshold If the situation can be determined with high confidence to be an abnormal solid-phase contact, the system will directly maintain a power-off state, prohibit the resumption of charging and discharging, and output a thermal runaway risk warning signal.

[0048] For example, the step threshold needs to be calibrated in the initial healthy state of the lithium battery when it is not in operation and there are no abnormal deposits or contact behaviors inside. Before the calibration test, the battery is subjected to static activation treatment, and the internal interface state of the battery is detected by electrochemical impedance spectroscopy (EIS) to confirm that there are no problems such as abnormal solid phase deposition or electrode protrusion, ensuring that the test starts in a healthy state. The specific calibration method is as follows: multi-cycle pulse charge-discharge test is performed within the full operating temperature range, using a low-rate pulse charge-discharge mode, while controlling the charge-discharge cutoff voltage to not exceed the normal operating voltage range of the battery to prevent overcharging from causing electrode interface damage and abnormal solid phase growth. During the battery charge-discharge operation, broadband light is input to the probe to collect recovery rate sample data dominated by changes in the liquid phase environment. Specifically, the radiation mode intensity signal Is(t) and the core mode intensity signal Ip(t) are collected simultaneously, the corresponding discrimination coefficient K(t) is calculated, the mean and variance of K(t) are statistically analyzed, and a signal-to-noise ratio threshold for judging the step change of K(t) is set to determine the step threshold. Based on the determined step threshold, dynamic recovery characteristic testing is performed. According to step S4, when the discrimination coefficient exceeds the step threshold, a pause charge / discharge command is sent to the battery management system. The discrimination coefficient is continuously recorded within a set time window, and the recovery rate of the discrimination coefficient within that time window is calculated. A normal distribution is fitted to the recovery rate, and the mean μ and standard deviation σ of the liquid phase recovery rate are calculated. Based on the 3σ criterion, the judgment threshold is set to... Achieve high-confidence discrimination of solid-phase anomalies.

[0049] It should be noted that different battery systems, such as ternary lithium and lithium iron phosphate, have different electrolyte viscosity, conductivity, and ion diffusion characteristics, resulting in significant differences in the recovery behavior of the liquid phase environment after power failure. Therefore, threshold calibration is required for the specific battery system before use.

[0050] The above calibration method can determine the basic step threshold, ensuring a high-confidence distinction between liquid and solid phase anomalies under standard operating conditions. However, in practical applications, batteries often operate under complex conditions with different temperatures and charge / discharge rates. These conditions affect the electrolyte ion diffusion rate, leading to natural fluctuations in the recovery rate of liquid phase anomalies. Therefore, the step threshold needs to be dynamically and adaptively corrected to adapt to the requirements of multi-condition operation. Specifically, this includes: obtaining real-time temperature and charge / discharge rate data during battery operation from the battery management system; and appropriately lowering the threshold when a decrease in battery temperature is detected, which leads to increased electrolyte viscosity and hindered ion diffusion. The natural decrease in recovery rate is allowed, reducing the probability of false alarms at low temperatures (the effect of temperature on the signal has been decoupled through the P-polarization channel); when an increase in battery temperature is detected, the diffusion of electrolyte ions accelerates, correspondingly improving... To maintain the ability to recognize weak solid-phase contact signals; and to combine the effect of charge / discharge rate on ion concentration polarization, to Auxiliary corrections are made to achieve reliable judgment under a wide range of operating conditions.

[0051] For example, the battery temperature and charge / discharge rate are monitored in real time. When the battery temperature exceeds a set temperature range, the judgment threshold is adjusted according to a set temperature coefficient. Then, it is determined whether the charge / discharge rate exceeds a set rate range. If it does, the judgment threshold is adjusted according to a set rate coefficient. Both the temperature coefficient and the rate coefficient are based on experimental calibration: The entire operating temperature range of the battery is selected, and multiple sets of liquid phase anomaly recovery rate tests are conducted at different temperature points using a reference temperature as a benchmark. The correction ratio of the judgment threshold for every 10°C temperature change is obtained through fitting, which is the temperature coefficient. This coefficient is negative when the temperature decreases and positive when the temperature increases. Covering the commonly used charge / discharge rate range of the battery, using a reference rate as a benchmark, the fluctuation pattern of the liquid phase anomaly recovery rate at different rates is tested. The correction ratio of the judgment threshold for every unit deviation of the rate from the reference rate is obtained through fitting, which is the rate coefficient. The coefficient is positive when the rate decreases.

[0052] In some embodiments, to proactively avoid potential battery safety hazards, the evolution trend of solid-phase anomalies in the battery is analyzed to mitigate these hazards. Specifically, the recovery rate of each solid-phase anomaly event is recorded during the battery's entire lifespan charge-discharge cycle. The criteria for determining the battery health status include: discriminant coefficient offset, occurrence time, and duration. The abnormal duration is the time interval of abnormal signal fluctuation, i.e., from the occurrence of a significant step shift in the discriminant coefficient until it stabilizes at a new equilibrium value; the discriminant coefficient offset is the difference between the real-time discriminant coefficient and the step threshold at the time of the abnormal event. The cumulative occurrence frequency, discriminant coefficient offset, and duration of solid-phase abnormal events are fitted with the variation patterns of charge-discharge cycles. Based on the trends of at least two of these factors, a graded early warning system for battery health status is established. For example, if both the cumulative occurrence frequency and the discriminant coefficient offset show an increasing trend, it indicates an increase in lithium deposition inside the battery, continuous growth of solid-phase protrusions, and a continuous decline in battery health. If both the cumulative occurrence frequency and the discriminant coefficient offset are stable, it indicates that the solid-phase abnormality is in a stable state and requires continuous monitoring. If both the cumulative occurrence frequency and the discriminant coefficient offset show a decreasing trend, it indicates that the solid-phase abnormality has no further evolution risk, and the monitoring frequency can be appropriately reduced.

[0053] Based on the aforementioned evolutionary trend, some embodiments also establish a graded early warning mechanism to link the battery management system to execute graded protection measures. Specifically, graded thresholds are set for cumulative occurrence frequency and discrimination coefficient offset to distinguish between mild, moderate, and severe solid phase anomalies, or more levels of anomalies. For example, the criteria for determining mild solid phase anomalies are: the K(t) step offset of a single solid phase anomaly is less than the preset mild threshold, the cumulative occurrence frequency does not exceed 5 times per 100 charge-discharge cycles, and there is no obvious increasing trend; the criteria for determining moderate solid phase anomalies are: the K(t) step offset of a single solid phase anomaly reaches the moderate threshold, the cumulative occurrence frequency is 5-15 times per 100 charge-discharge cycles, or the signal strength shows a slow increasing trend; the criteria for determining severe solid phase anomalies are: the K(t) step offset of a single solid phase anomaly exceeds the severe threshold, the cumulative occurrence frequency exceeds 15 times per 100 charge-discharge cycles, or signals related to severe lithium deposition or electrode particle cracking are detected.

[0054] The above process constitutes a full lifecycle safety management mechanism based on historical monitoring data. In the early stages of actual battery operation, a small number of occasional abnormal deposition events may gradually disappear during subsequent operation. Although this may cause some capacity decay, it usually does not immediately lead to internal short-circuit risks. However, when the system detects a continuous upward trend in the recurrence frequency of low recovery rate events, it indicates that the uniformity of lithium deposition on the innermost negative electrode surface of the wound cell is gradually deteriorating, and the risk of stable solid-phase contact anomalies inside the battery is significantly increased. In this case, the system outputs graded warnings and corresponding control commands based on the nature and severity of the abnormal events. For example, the protective measures corresponding to mild solid-phase anomalies are: reducing the charging rate to 70%-80% of the normal rate, while shortening the charge-discharge cycle interval, increasing the resting time, alleviating electrolyte concentration polarization, and inhibiting further growth of solid-phase anomalies such as lithium deposition, without affecting the normal use of the battery. The protective measures for moderate solid phase anomalies are as follows: extend the power-off resting time to 2-3 times the normal resting time, implement a restricted operation mode, limit the battery charge / discharge rate to no more than 0.5C, reduce stress concentration and ion accumulation at the electrode interface, slow down the evolution rate of solid phase anomalies, and continuously increase the frequency of real-time monitoring. The protective measures for severe solid phase anomalies are as follows: maintain the power-off state directly, prohibit battery charging and discharging, and simultaneously output a thermal runaway risk warning to the battery management system and terminal equipment to remind personnel to handle the situation promptly and avoid safety accidents such as internal short circuits and thermal runaway.

[0055] The scope of protection of this invention is defined only by the claims. Thanks to the teachings of this invention, those skilled in the art will readily recognize that alternative structures to the structures disclosed herein can be used as feasible alternative implementations, and that the implementations disclosed herein can be combined to produce new implementations, which also fall within the scope of the appended claims.

Claims

1. An in-situ monitoring device for the internal state of a lithium battery, characterized in that, The device includes a fiber Bragg grating sensing probe, which is inserted into the central axial cavity of a cylindrical lithium battery. One end of the probe passes through the battery top cover and connects to a signal demodulation unit, while the other end is suspended within the cavity. The probe includes an optical fiber with a grating etched on it at a 45° angle to its cross-section, enabling it to separate the optical signal into a radiation mode intensity signal and a core mode intensity signal. The signal demodulation unit is configured to simultaneously acquire the radiation mode intensity signal and the core mode intensity signal, perform a ratio calculation, and obtain a real-time discrimination coefficient. Based on the changing trend of the discriminant coefficient, determine whether there is an anomaly.

2. The in-situ monitoring device for the internal state of a lithium battery as described in claim 1, characterized in that, The battery top cover has holes for probes to pass through and a sealing assembly.

3. The in-situ monitoring device for the internal state of a lithium battery as described in claim 1, characterized in that, The fiber optic cable suspended in the cavity has a spherical end cap.

4. The in-situ monitoring device for the internal state of a lithium battery as described in claim 3, characterized in that, The distal spherical cap surface is coated with a metal reflective film.

5. The in-situ monitoring device for the internal state of a lithium battery as described in claim 1, characterized in that, Determining whether there is a potential anomaly based on the changing trend of the discrimination coefficient includes: continuously monitoring the difference between the real-time value of the discrimination coefficient and the value at the previous moment; if the absolute value of the difference is greater than a preset step threshold and the difference continues to remain for more than a set time, it is determined that there is a potential anomaly.

6. The in-situ monitoring device for the internal state of a lithium battery as described in claim 5, characterized in that, The method for determining the step threshold is as follows: under the battery health state, simultaneously collect radiation mode intensity signal and fiber core mode intensity signal, and calculate the corresponding discrimination coefficient; The step threshold is determined based on the mean and variance of the discrimination coefficients.

7. The in-situ monitoring device for the internal state of a lithium battery as described in claim 6, characterized in that, When a potential anomaly is detected, a charge / discharge pause command is sent to the battery management system. The discrimination coefficient is continuously recorded within a set time window, and the recovery rate of the discrimination coefficient within that time window is calculated. If the recovery rate is higher than the set judgment threshold, the anomaly is determined to be caused by a change in the liquid phase environment; otherwise, the anomaly is determined to be caused by an anomaly in the solid phase structure.

8. The in-situ monitoring device for the internal state of a lithium battery as described in claim 7, characterized in that, The method for determining the judgment threshold is as follows: under the battery health state, simultaneously collect radiation mode intensity signal and fiber core mode intensity signal, and calculate the real-time discrimination coefficient; When the discrimination coefficient exceeds the step threshold, a pause charge / discharge command is sent to the battery management system. The discrimination coefficient is continuously recorded within a set time window, and the recovery rate of the discrimination coefficient within the time window is calculated. The discrimination threshold is determined based on the mean and variance of the recovery rate.

9. The in-situ monitoring device for the internal state of a lithium battery as described in claim 7 or 8, characterized in that, If the abnormal event is caused by a change in the liquid phase environment, the charging current rate is reduced after the battery resumes operation; if the abnormal event is caused by an abnormal solid phase structure, if the recovery rate does not reach the critical threshold, the power-off settling time is extended, and operation is resumed after the discrimination coefficient stabilizes; if the recovery rate reaches the critical threshold, the power-off state is maintained.

10. The in-situ monitoring device for the internal state of a lithium battery as described in claim 7 or 8, characterized in that, The method further includes: acquiring historical solid-phase abnormal events, and classifying and issuing early warnings on the health status of the battery based on the changing trends of at least two of the following: cumulative occurrence frequency, discrimination coefficient offset, and event duration.

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