Preparation method of thin film sensor integrated with temperature and pressure monitoring and self-heating functions and application thereof in battery system

Abstract

The application relates to a preparation method of a thin film sensor integrated with temperature and pressure monitoring and self-heating functions and application of the thin film sensor in a battery system. The method comprises the following steps: S1, preparing a sensitive material; S2, preparing a sensitive thin film; and S3, preparing a thin film sensor. The thin film sensor integrated with temperature and pressure monitoring and self-heating functions is used for monitoring temperature and pressure in the battery system. The application designs and prepares a thin film sensor integrated with temperature and pressure monitoring and self-heating functions, which can effectively monitor battery temperature and inter-battery cell pressure, reflect the internal state of the battery cell, and keep the battery at an optimal operating temperature in a low-temperature environment. The preparation method is simple and easy to implement, low in cost, wide in applicability, and can be applied on a large scale.

Description

Technical Field

[0001] This invention relates to a method for fabricating a thin-film sensor and its application. Background Technology

[0002] With the ongoing global energy structure transformation, lithium-ion batteries, with their advantages of high energy density and long cycle life, have been widely used in new energy vehicles, energy storage power stations, and portable electronic devices. Currently, the low-altitude economy is experiencing rapid development, and the basic equipment for the low-altitude economy, such as drones and small aircraft, will mainly rely on lithium-ion batteries for power. Under normal operating conditions, the internal electrochemical reactions of lithium-ion batteries are stable and reversible, and internal heat is conserved. However, lithium batteries are prone to thermal runaway under overcharging, over-discharging, mechanical abuse, or extreme temperature conditions, leading to safety accidents such as combustion and explosion. Among these, lithium plating and increased internal resistance caused by low-temperature environments, and a sudden increase in internal pressure under high-temperature conditions have been proven to be two key factors inducing thermal runaway in non-human-caused situations. Therefore, monitoring the battery's operating status, real-time monitoring of its internal temperature and pressure, and maintaining it at the optimal operating temperature are crucial for ensuring battery safety and improving battery charge and discharge performance. This is also a key research direction for the future development of lithium-ion batteries.

[0003] Currently, many research teams have conducted extensive research and experiments on battery health monitoring for battery status detection. The latest research advancements include multimodal data-driven early warning, battery health estimation under limited physical sensing, and monitoring through internal battery sensor implantation. For data-driven battery status early warning, acquiring battery status parameters requires high-precision, high-real-time sensors to monitor the current battery operating state. Traditional detection schemes rely solely on temperature sensors attached to the battery module casing to detect module surface temperature, which impacts accuracy and real-time performance. Furthermore, there is currently no mature method for detecting battery pressure signals. Therefore, schemes based on internally implanted sensors for monitoring battery status have been widely studied, such as embedding fiber optic sensors between electrode plates. While this effectively monitors internal temperature and pressure changes, its high cost and complex supporting equipment hinder its large-scale application. Compared to fiber optic sensors, thin-film sensors, due to their flatness, thinness, and flexibility, can be implanted inside battery modules or even within battery cells. Although current thin-film sensors have simple fabrication processes and acquisition methods, their limited parameters and low integration restrict their application in various scenarios. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a method for fabricating a thin-film sensor that integrates temperature and pressure monitoring and self-heating functions, and its application in a battery system.

[0005] A method for fabricating a thin-film sensor integrating temperature and pressure monitoring and self-heating functions is specifically carried out according to the following steps:

[0006] I. Preparation of Sensitive Materials:

[0007] Chromium powder, PVDF powder and graphene powder are mixed and ground to obtain a mixed powder; N-methylpyrrolidone is added dropwise to the mixed powder and stirred to obtain a uniform and viscous slurry;

[0008] II. Preparation of sensitive thin films:

[0009] The slurry is coated onto a polyimide film, then dried, and the film formed by the slurry is separated from the polyimide film to obtain a chromium powder / PVDF / graphene composite sensitive material film.

[0010] III. Fabrication of Thin-Film Sensors:

[0011] Excess copper foil is etched away on a polyimide substrate with copper foil on its surface using a laser etching machine, leaving interdigitated electrode copper wire pathways. Then, a chromium powder / PVDF / graphene composite sensing material film is applied to the interdigitated electrode copper wire pathways. Polyimide tape is then used to adhere and cover the polyimide substrate, forming a structure from bottom to top consisting of a polyimide substrate, interdigitated electrode copper wire pathways, composite sensing material film, and polyimide tape. Finally, a PT1000 temperature sensor is welded to the bottom of the interdigitated electrode copper wire pathways to obtain a thin-film sensor integrating temperature and pressure monitoring and self-heating functions.

[0012] Thin-film sensors integrating temperature and pressure monitoring and self-heating functions monitor temperature and pressure in battery systems and provide in-situ internal heating of the battery in low-temperature environments.

[0013] Advantages of this invention:

[0014] I. This invention designs and fabricates a thin-film sensor that integrates temperature and pressure monitoring and self-heating functions. It can effectively monitor battery temperature and inter-cell pressure to reflect the internal state of the cell. It can also keep the battery at its optimal operating temperature in low-temperature environments. The fabrication method of this invention is simple and easy to implement, low in cost, widely applicable, and can be used on a large scale.

[0015] Second, the pressure-sensitive performance of the thin-film sensor with integrated temperature and pressure monitoring and self-heating function prepared by the present invention was tested. The results showed that the pressure sensitivity range of the sensor is (0-170kPa), and the response and recovery times are 700ms and 100ms, respectively. In addition, while possessing pressure-sensitive characteristics, the sensor can also preheat and heat the battery internally through Joule heating, maintaining the battery in a stable temperature range and extending the battery life. Attached Figure Description

[0016] Figure 1The images are SEM images, where (a) shows chromium powder particles with irregular shapes, (b) is a planar SEM image of the chromium powder / PVDF / graphene composite sensitive material film prepared in step two of Example 1, (c) is a cross-sectional SEM image of the chromium powder / PVDF / graphene composite sensitive material film prepared in step two of Example 1, and (d) is an enlarged cross-sectional view of the chromium powder / PVDF / graphene composite sensitive material film prepared in step two of Example 1.

[0017] Figure 2 The images show the physical optical photographs of the thin-film sensor with integrated temperature and pressure monitoring and self-heating functions prepared in step three of Example 1, and the PT1000 welding sites, where (a) is an optical photograph of the front of the sensor and (b) is a photograph of the back.

[0018] Figure 3 The structure and dimensions of the thin-film sensor with integrated temperature and pressure monitoring and self-heating functions prepared in step three of Example 1 are shown, where (a) is the sensor size and (b) is the sensor structure diagram.

[0019] Figure 4 The current response curve of the thin-film sensor with integrated temperature and pressure monitoring and self-heating functions prepared in step three of Example 1 is shown as a function of applied pressure.

[0020] Figure 5 This is the real-time response signal of the thin-film sensor with integrated temperature and pressure monitoring and self-heating functions prepared in step three of Example 1 under transient pressure;

[0021] Figure 6 The sensitivity test of the thin-film sensor with integrated temperature and pressure monitoring and self-heating function prepared in step three of Example 1 under high initial pressure, where (a) represents a press test of ±0.3 kPa at 30 kPa pressure, and (b) represents a press test of ±0.6 kPa at an initial pressure of 60 kPa.

[0022] Figure 7 The signal changes of the PT1000 temperature unit are shown under ambient temperature variations of 25℃-80℃, and the pressure signal changes of the thin-film sensor with integrated temperature and pressure monitoring and self-heating functions prepared in step three of Example 1 under loads of 0.1 kPa (Loading 0.1 kPa) and 0.6 kPa (Loading 0.6 kPa).

[0023] Figure 8 The pressure cycling and temperature drift stability of the thin-film sensor with integrated temperature and pressure monitoring and self-heating functions prepared in step three of Example 1;

[0024] Figure 9This experiment involved applying a gradient pressure signal while simultaneously applying pressure and temperature variations to the thin-film sensor with integrated temperature and temperature monitoring and self-heating functions prepared in step three of Example 1.

[0025] Figure 10 This is a test image of the low-temperature heating effect of the thin-film sensor with integrated temperature and pressure monitoring and self-heating function, prepared in step three of Example 1, embedded in a soft-pack battery.

[0026] Figure 11 This is a battery cycle test experiment of the thin-film sensor with integrated temperature and pressure monitoring and self-heating function prepared in step three of Example 1 under three different temperature conditions. In the experiment, the battery was charged and discharged at a rate of 0.2C for 50 cycles. Among them, (a) is the voltage and capacity curve of the battery under three conditions: room temperature 25℃ (Normal), -20℃, and heating from -20℃ to +20℃ by activating the sensor heating function. (b) is a comparison graph of the changes in coulombic efficiency under the three conditions. Detailed Implementation

[0027] Specific Implementation Method 1: This implementation method is a fabrication method for a thin-film sensor integrating temperature and pressure monitoring and self-heating functions, specifically completed according to the following steps:

[0028] I. Preparation of Sensitive Materials:

[0029] Chromium powder, PVDF powder and graphene powder are mixed and ground to obtain a mixed powder; N-methylpyrrolidone is added dropwise to the mixed powder and stirred to obtain a uniform and viscous slurry;

[0030] II. Preparation of sensitive thin films:

[0031] The slurry is coated onto a polyimide film, then dried, and the film formed by the slurry is separated from the polyimide film to obtain a chromium powder / PVDF / graphene composite sensitive material film.

[0032] III. Fabrication of Thin-Film Sensors:

[0033] Excess copper foil is etched away on a polyimide substrate with copper foil on its surface using a laser etching machine, leaving interdigitated electrode copper wire pathways. Then, a chromium powder / PVDF / graphene composite sensing material film is applied to the interdigitated electrode copper wire pathways. Polyimide tape is then used to adhere and cover the polyimide substrate, forming a structure from bottom to top consisting of a polyimide substrate, interdigitated electrode copper wire pathways, composite sensing material film, and polyimide tape. Finally, a PT1000 temperature sensor is welded to the bottom of the interdigitated electrode copper wire pathways to obtain a thin-film sensor integrating temperature and pressure monitoring and self-heating functions.

[0034] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the mass ratio of chromium powder, PVDF powder, and graphene powder in step one is (0.5~1.5):10:(3~5). The other steps are the same as in Specific Implementation Method One.

[0035] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that the grinding time in step one is 30 to 60 minutes. Other steps are the same as in Specific Implementation Method One or Two.

[0036] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the stirring time in step one is 10-12 hours. The other steps are the same as in Specific Implementation Methods One to Three.

[0037] Specific Implementation Method Five: The difference between this implementation method and Specific Implementation Methods One to Four is that the mass ratio of the mixed powder to the volume ratio of N-methylpyrrolidone in step one is (14g~16g):20mL. The other steps are the same as in Specific Implementation Methods One to Four.

[0038] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the coating speed in step two is 1 cm / s, and the coating thickness is 20 μm to 100 μm. The other steps are the same as in Specific Implementation Methods One to Five.

[0039] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that: the thickness of the polyimide film mentioned in step two is 100 micrometers; the drying temperature mentioned in step two is 80℃~100℃, and the drying time is 20h~24h. Other steps are the same as in Specific Implementation Methods One to Six.

[0040] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that the thickness of the polyimide substrate in step three is 12.5 μm, and the thickness of the surface copper foil is 18 μm. The other steps are the same as in Specific Implementation Methods One to Seven.

[0041] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that: the polyimide substrate described in step three includes a circular working area and a strip-shaped lead-out area, wherein the diameter of the circular working area is 28 mm, the interdigitated electrode copper wire passage is disposed within the circular working area with a diameter of 19 mm, the diameter of the chromium powder / PVDF / graphene composite sensitive material film is 19 mm, and the diameter of the polyimide tape is 28 mm. Other steps are the same as in Specific Implementation Methods One to Eight.

[0042] Specific Implementation Method 10: This implementation method integrates a thin-film sensor with temperature and pressure monitoring and self-heating functions to monitor temperature and pressure in the battery system and perform in-situ internal heating of the battery in a low-temperature environment.

[0043] The beneficial effects of the present invention are verified using the following embodiments:

[0044] Example 1: A method for fabricating a thin-film sensor integrating temperature and pressure monitoring and self-heating functions, specifically completed according to the following steps:

[0045] I. Preparation of Sensitive Materials:

[0046] Mix 1g of chromium powder, 10g of PVDF powder and 4g of graphene powder, grind for 40min to obtain a mixed powder; add 20mL of N-methylpyrrolidone dropwise to the mixed powder, stir for 12h to obtain a uniform and viscous slurry;

[0047] II. Preparation of sensitive thin films:

[0048] The slurry was poured onto a 100-micron thick polyimide film, and the film was scraped using an automatic scraper with a thickness of 20 microns and a scraping speed of 1 cm / s. The film was then dried at 90°C for 24 hours. The film formed by the slurry was then separated from the polyimide film to obtain a chromium powder / PVDF / graphene composite sensitive material film.

[0049] III. Fabrication of Thin-Film Sensors:

[0050] Excess copper foil was etched away from a copper-coated polyimide substrate using a laser etching machine, leaving interdigitated electrode copper wire pathways. A chromium powder / PVDF / graphene composite sensing material film was then applied over these pathways. Polyimide tape was then used to adhere and cover the polyimide substrate, forming a structure from bottom to top consisting of the polyimide substrate, interdigitated electrode copper wire pathways, composite sensing material film, and polyimide tape. A PT1000 temperature sensor was then welded to the bottom of the interdigitated electrode copper wire pathways, resulting in a thin-film sensor integrating temperature and pressure monitoring and self-heating functions. (See...) Figure 2 and Figure 3 As shown;

[0051] The polyimide substrate mentioned in step three has a thickness of 12.5 μm, and the copper foil on the surface has a thickness of 18 μm;

[0052] The polyimide substrate described in step three includes a circular working area and a strip-shaped lead-out area. The diameter of the circular working area is 28 mm. The interdigitated electrode copper wire path is set in the circular working area with a diameter of 19 mm. The diameter of the chromium powder / PVDF / graphene composite sensitive material film is 19 mm, and the diameter of the polyimide tape is 28 mm.

[0053] Figure 1 The images are SEM images, where (a) shows chromium powder particles with irregular shapes, (b) is a planar SEM image of the chromium powder / PVDF / graphene composite sensitive material film prepared in step two of Example 1, (c) is a cross-sectional SEM image of the chromium powder / PVDF / graphene composite sensitive material film prepared in step two of Example 1, and (d) is an enlarged cross-sectional view of the chromium powder / PVDF / graphene composite sensitive material film prepared in step two of Example 1.

[0054] from Figure 1 As can be seen, chromium powder particles are tightly coated or anchored within the graphene mesh. This composite mode of "nanofiber entangled with micron-sized particles" effectively prevents the agglomeration of inorganic powders in the polymer matrix. Chromium powder (Cr) particles, acting as conductive fillers, uniformly fill the porous network constructed by graphene, significantly increasing the number of contact sites in the conductive path. These particles form numerous microscopic contact interfaces with graphene, which is the core region for the piezoresistive effect. Simultaneously, a small amount of chromium powder particles provides a negative temperature coefficient, significantly suppressing sensor temperature drift within the battery's operating temperature range. The continuous smooth region shown in the cross-sectional SEM image of the thin film represents the PVDF polymer matrix. PVDF not only acts as a binder to firmly fix the conductive fillers (graphene powder and chromium powder) onto the polyimide substrate but also provides deformation space for the material through its excellent flexibility. The interface between the conductive filler and the PVDF matrix is ​​blurred and tightly bonded, with no obvious cracks or voids observed. This excellent interface compatibility ensures that the internal conductive network of the sensor will not be mechanically stripped when subjected to cyclic pressure shocks, thus ensuring the sensor's excellent cyclic stability.

[0055] Figure 2 The images show the physical optical photographs of the thin-film sensor with integrated temperature and pressure monitoring and self-heating functions prepared in step three of Example 1, and the PT1000 welding sites, where (a) is an optical photograph of the front of the sensor and (b) is a photograph of the back.

[0056] from Figure 2 As can be seen, the thin-film sensor with integrated temperature and pressure monitoring and self-heating functions prepared in step three of Example 1 is generally a black thin film (sensitive layer), and the substrate is a polyimide substrate with copper foil on the surface. The sensor is extremely thin (about 80 micrometers) with a smooth and flat surface, and exhibits excellent mechanical flexibility, maintaining its structural integrity even when bent or rolled. This allows it to perfectly fit onto the surface of a lithium-ion battery cell or be wound inside the cell without damaging the original mechanical structure of the battery. To increase the temperature parameter, a standard industrial-grade PT1000 temperature sensor (platinum resistance thermometer) is soldered to the sensor circuit as a temperature signal acquisition element. The PT1000 is tightly attached to the surface of the thin-film sensor.

[0057] Figure 3 The structure and dimensions of the thin-film sensor with integrated temperature and pressure monitoring and self-heating functions prepared in step three of Example 1 are shown, where (a) is the sensor size and (b) is the sensor structure diagram.

[0058] Figure 3 The multilayer structure design of the thin-film sensor with integrated temperature and pressure monitoring and self-heating function prepared in step three of Example 1 is shown in detail. The sensor adopts a sandwich structure of "substrate-electrode circuit-sensitive thin film-encapsulation layer".

[0059] in Figure 3 (a) is the sensor size, where the diameter A of the polyimide substrate is 28 mm, the diameter B of the sensitive film is 19 mm, the sensitive material completely covers the copper wire path of the interdigital electrode, the diameter of the outermost copper wire forming the ring of the interdigital electrode is 19 mm, the line width of the interdigital electrode copper wire is 0.15 mm, the interdigital electrode spacing C is 0.5 mm, the width D of the substrate on the signal output side is 5 mm, and the spacing E of the copper wires on the signal output side is 1 mm. Figure 3 (b) is a diagram of the sensor structure. As shown in the figure, the bottom layer is a polyimide substrate containing interdigitated electrode copper wire pathways.

[0060] The interdigitated electrode copper wire pathway is designed with a double-helix interdigitated structure to maximize the sensitive area. The middle layer is a chromium powder / PVDF / graphene composite sensitive material film. The upper layer is a polyimide tape (PI insulating tape) that bonds the sensitive material to the substrate. When the battery experiences a thermal runaway precursor leading to an increase in internal pressure, or is subjected to external mechanical compression, a pressure (P) perpendicular to the sensor surface acts on the sensitive film. This pressure causes the PVDF matrix to compress, forcing a reduction in the spacing between the internal graphene and chromium powder particles, significantly increasing the number of physical contact points. As the nanoparticle spacing shrinks to within the quantum tunneling distance, the electron tunneling effect is enhanced, and the number of conductive pathways increases exponentially. Macroscopically, this manifests as a sharp decrease in the sensor resistance (R) with increasing pressure, thus achieving sensitive pressure detection.

[0061] To evaluate the ability of this thin-film sensor to monitor changes in internal battery pressure (such as volume expansion due to lithium plating or pressure buildup due to thermal runaway), a systematic mechanical performance test was conducted on it.

[0062] Using a machine that applies controlled pressure, the thin-film sensor prepared in Example 1, which integrates temperature and pressure monitoring and self-heating functions, was gradually pressured to 150 kPa and then reduced to 0 kPa. The current-pressure variation curve was collected, as shown in the figure. Figure 4 As shown;

[0063] Figure 4 The current response curve of the thin-film sensor with integrated temperature and pressure monitoring and self-heating functions prepared in step three of Example 1 is shown as a function of applied pressure.

[0064] from Figure 4 As can be seen, the sensor exhibits a typical and excellent piezoresistive effect. Based on the sensitivity formula (ΔR / R0), the sensor's response range can be divided into two typical linear regions: a low-pressure high-sensitivity region (0-50 kPa): In this range, the curve slope is extremely steep, exhibiting extremely high sensitivity (S). This is because, during the initial pressurization stage, the loose contact between the graphene conductive network and chromium powder particles within the PVDF matrix rapidly transforms into a tight contact, resulting in a sharp decrease in contact resistance. This characteristic allows the sensor to extremely sensitively detect minute pressure fluctuations or early bulging phenomena inside the battery. A wide-range linear region (50-200 kPa): As the pressure further increases, the conductive path tends to saturate, and the rate of resistance change slows down but maintains a good linear relationship. This wide-range characteristic ensures that the sensor can still provide accurate pressure readings without signal saturation even when the battery experiences severe mechanical abuse or severe thermal runaway high-pressure shocks.

[0065] A machine for applying controllable pressure was used to momentarily apply a pressure of 50 kPa to the thin-film sensor prepared in Example 1, which integrates temperature and pressure monitoring and self-heating functions. The pressure was then released momentarily after 10 seconds, and the signal collected by the sensor was recorded. (See attached image.) Figure 5 As shown;

[0066] Figure 5 This is the real-time response signal of the thin-film sensor with integrated temperature and pressure monitoring and self-heating functions prepared in step three of Example 1 under transient pressure;

[0067] from Figure 5 It is evident that the sensor exhibits excellent response and recovery times. When a step pressure signal is applied, the sensor resistance responds within an extremely short time. Test data shows that its response time is less than 700ms and its recovery time is less than 100ms. This rapid response speed is crucial for capturing the pressure surge during battery thermal runaway, providing the Battery Management System (BMS) with valuable time for early warning and circuit disconnection.

[0068] An initial pressure of 30 kPa was applied to the thin-film sensor with integrated temperature and pressure monitoring and self-heating functions prepared in step three of Example 1 using a pressurizing device. Then, it was controlled to apply ±0.3 kPa fluctuations, i.e., cyclically inputting pressures of 29.7 kPa and 30.3 kPa. Similarly, at 60 kPa, it was controlled to apply ±0.6 kPa fluctuations, i.e., cyclically inputting pressures of 59.4 kPa and 60.6 kPa. (See...) Figure 6 As shown;

[0069] Figure 6The sensitivity test of the thin-film sensor with integrated temperature and pressure monitoring and self-heating function prepared in step three of Example 1 under high initial pressure, where (a) represents a press test of ±0.3 kPa at 30 kPa pressure, and (b) represents a press test of ±0.6 kPa at an initial pressure of 60 kPa.

[0070] Figure 6 The demonstration shows the sensor's signal performance under high initial pressure and small pressure variations. Figure 6 (a) indicates a pressurization test of ±0.3 kPa at a pressure of 30 kPa. Figure 6 (b) indicates that a pressure test of ±0.6 kPa was performed at an initial pressure of 60 kPa. The results show that the sensor can still maintain good pressure detection performance under high initial pressure.

[0071] The thin-film sensor with integrated temperature and pressure monitoring and self-heating functions, prepared in step three of Example 1, was placed in an oven. The oven temperature was raised from 25°C to 80°C. Pressures of 0.1 kPa and 0.6 kPa were applied twice, respectively, to obtain… Figure 7 The image shows the pressure signal under temperature changes;

[0072] Figure 7 The signal changes of the PT1000 temperature unit are shown under ambient temperature variations of 25℃-80℃, and the pressure signal changes of the thin-film sensor with integrated temperature and pressure monitoring and self-heating functions prepared in step three of Example 1 under loads of 0.1 kPa (Loading 0.1 kPa) and 0.6 kPa (Loading 0.6 kPa).

[0073] from Figure 7 It can be observed that although the background ambient temperature shifted significantly, the pressure signal did not shift significantly with temperature. This phenomenon proves that the piezoresistive effect of the conductive network inside the sensitive material layer dominates when subjected to compressive deformation, while the interference of geometric changes caused by thermal expansion or thermal excitation of charge carriers on the pressure signal is minimized.

[0074] The integrated pressure and temperature monitoring and self-heating thin-film sensor and PT1000 temperature sensor prepared in step three of Example 1 were placed in an oven. The oven temperature was controlled from 20°C to 80°C and then back to 20°C. Simultaneously, a vibration of 50 kPa ± 1 kPa was applied to the sensor. The cycle test exceeded 11850 s. (See attached image.) Figure 8 As shown;

[0075] Figure 8The pressure cycling and temperature drift stability of the thin-film sensor with integrated temperature and pressure monitoring and self-heating functions prepared in step three of Example 1;

[0076] Figure 8 The pressure cycling and temperature drift stability of the sensor were demonstrated. After multiple continuous pressurization / depressurization cycles with temperature variations of 20℃-80℃-20℃, no significant drift was observed in the initial resistance and response amplitude of the sensor. This proves that the chromium powder / PVDF / graphene composite sensing material film has excellent fatigue resistance and can meet the long-term monitoring needs throughout the entire life cycle of lithium-ion batteries.

[0077] Figure 9 This experiment involved applying a gradient pressure signal while simultaneously applying pressure and temperature variations to the thin-film sensor with integrated temperature and temperature monitoring and self-heating functions prepared in step three of Example 1.

[0078] Figure 9 This indicates the change in the sensor's sampled signal when the sensor is in heating mode, i.e., when voltage is applied to the sensor. The experiment applied voltages of 1V, 2V, 3V, 4V, and 5V to the sensor, resulting in heating effects of 20℃, 25℃, 30℃, 40℃, and 50℃ at room temperature, respectively. The experimental results show that a clear gradient pressure signal is observed when pressure is applied to the sensor, indicating that good pressure signal changes are still visible even in heating mode.

[0079] Figure 10 This is a test image of the low-temperature heating effect of the thin-film sensor with integrated temperature and pressure monitoring and self-heating function, prepared in step three of Example 1, embedded in a soft-pack battery.

[0080] Figure 10 This image shows a thermal image of the thin-film sensor with integrated temperature and pressure monitoring and self-heating functions, prepared in step three of Example 1, after being implanted into a pouch battery under low-temperature heating mode. To achieve large-area and uniform in-situ heating inside the battery, five thin-film sensors prepared in this example were simultaneously attached to the battery surface in a symmetrical distribution of 'four corners plus the center', and these five sensors were connected in parallel to an external constant current source drive circuit for coordinated heating. Figure 10 (a) When the ambient temperature is -5°C, the sensor is used to heat the battery to keep it at 25°C. The total power required for heating is 10W. Figure 10 (b) To maintain the battery at 25°C using sensor heating at an ambient temperature of -12°C, the total power required for heating is 11W. Figure 10 (c) To maintain the battery temperature at 25°C using sensor heating at an ambient temperature of -18°C, the total power required for heating is 13W. Figure 10 (d) The battery is kept at 25°C by using sensor heating at an ambient temperature of -24°C. The total power required for heating at this time is 19W.

[0081] Figure 11 This is a battery cycle test experiment of the thin-film sensor with integrated temperature and pressure monitoring and self-heating function prepared in step three of Example 1 under three different temperature conditions. In the experiment, the battery was charged and discharged at a rate of 0.2C for 50 cycles. Among them, (a) is the voltage and capacity curve of the battery under three conditions: room temperature 25℃ (Normal), -20℃, and heating from -20℃ to +20℃ by turning on the sensor heating function. (b) is a comparison graph of the changes in coulombic efficiency under the three conditions.

[0082] from Figure 11 (a) It can be seen that in the experiment of 50 charge-discharge cycles, the battery voltage window under the low temperature environment of -20℃ narrowed rapidly over time, and the capacity also decreased rapidly. The battery under room temperature and the battery under sensor heating mode maintained good operating condition. Figure 11 (b) shows a comparison of coulombic efficiency changes under three conditions. It can be seen that the battery coulombic efficiency at -20℃ decreases significantly with increasing cycle number, while the battery in sensor heating mode shows a coulombic efficiency curve that is essentially the same as that at room temperature. The experimental results demonstrate that enabling the sensor heating mode allows the battery to maintain good performance and lifespan even at low temperatures.

Claims

1. A method for fabricating a thin-film sensor integrating temperature and pressure monitoring and self-heating functions, characterized in that... The preparation method is specifically carried out according to the following steps: I. Preparation of Sensitive Materials: Chromium powder, PVDF powder and graphene powder are mixed and ground to obtain a mixed powder; N-methylpyrrolidone is added dropwise to the mixed powder and stirred to obtain a uniform and viscous slurry; II. Preparation of sensitive thin films: The slurry is coated onto a polyimide film, then dried, and the film formed by the slurry is separated from the polyimide film to obtain a chromium powder / PVDF / graphene composite sensitive material film. III. Fabrication of Thin-Film Sensors: Excess copper foil is etched away on a polyimide substrate with copper foil on its surface using a laser etching machine, leaving interdigitated electrode copper wire pathways. Then, a chromium powder / PVDF / graphene composite sensing material film is applied to the interdigitated electrode copper wire pathways. Polyimide tape is then used to adhere and cover the polyimide substrate, forming a structure from bottom to top consisting of a polyimide substrate, interdigitated electrode copper wire pathways, composite sensing material film, and polyimide tape. Finally, a PT1000 temperature sensor is welded to the bottom of the interdigitated electrode copper wire pathways to obtain a thin-film sensor integrating temperature and pressure monitoring and self-heating functions.

2. The method for fabricating a thin-film sensor integrating temperature and pressure monitoring and self-heating functions according to claim 1, characterized in that... The mass ratio of chromium powder, PVDF powder and graphene powder mentioned in step one is (0.5~1.5):10:(3~5).

3. The method for fabricating a thin-film sensor integrating temperature and pressure monitoring and self-heating functions according to claim 1, characterized in that... The grinding time mentioned in step one is 30 min to 60 min.

4. The method for fabricating a thin-film sensor integrating temperature and pressure monitoring and self-heating functions according to claim 1, characterized in that... The stirring time mentioned in step one is 10h~12h.

5. The method for fabricating a thin-film sensor integrating temperature and pressure monitoring and self-heating functions according to claim 1, characterized in that... The mass ratio of the mixed powder to the volume of N-methylpyrrolidone in step one is (14g~16g):20mL.

6. The method for fabricating a thin-film sensor integrating temperature and pressure monitoring and self-heating functions according to claim 1, characterized in that... The coating speed in step two is 1 cm / s, and the coating thickness is 20 μm to 100 μm.

7. The method for fabricating a thin-film sensor integrating temperature and pressure monitoring and self-heating functions according to claim 1, characterized in that... The thickness of the polyimide film mentioned in step two is 100 micrometers; the drying temperature mentioned in step two is 80℃~100℃, and the drying time is 20h~24h.

8. The method for fabricating a thin-film sensor integrating temperature and pressure monitoring and self-heating functions according to claim 1, characterized in that... The polyimide substrate mentioned in step three has a thickness of 12.5 μm, and the copper foil on the surface has a thickness of 18 μm.

9. The method for fabricating a thin-film sensor integrating temperature and pressure monitoring and self-heating functions according to claim 1, characterized in that... The polyimide substrate described in step three includes a circular working area and a strip-shaped lead-out area. The diameter of the circular working area is 28 mm. The interdigitated electrode copper wire path is set in the circular working area with a diameter of 19 mm. The diameter of the chromium powder / PVDF / graphene composite sensitive material film is 19 mm, and the diameter of the polyimide tape is 28 mm.

10. The application of the thin-film sensor with integrated temperature and pressure monitoring and self-heating functions prepared by the preparation method according to any one of claims 1 to 9, characterized in that... Thin-film sensors integrating temperature and pressure monitoring and self-heating functions monitor temperature and pressure in battery systems and provide in-situ internal heating of the battery in low-temperature environments.

Images