Soft package lithium battery internal and external temperature real-time monitoring method

Abstract

The invention relates to a soft package lithium battery internal and external temperature real-time monitoring method, which comprises the following steps of: in a soft package battery packaging process, implanting a plurality of superfine thermocouples into a key area in a battery to obtain a temperature change condition in the battery; the key area comprises an area below the current collector, a maximum thickness position and an area close to the bottom of the shell; meanwhile, a plurality of distributed temperature measuring points are arranged on the outer surface of the battery, superfine thermocouples are arranged respectively, a distributed monitoring network is formed, and the temperature change condition outside the battery is obtained; the proportion of the total volume of the implanted superfine thermocouple to the internal space of the battery is lt; 0.03% by weight; temperature data are recorded in real time through high-precision acquisition equipment, the sampling frequency is adjustable, and the temperature error does not exceed + / -0.01 DEG C. By optimizing a sensor arrangement strategy, the original performance of the battery is maintained to the maximum extent while accurate temperature monitoring is achieved, and the method is suitable for temperature field accurate management and thermal safety control in the fields of power batteries, energy storage batteries and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium battery temperature monitoring, and particularly relates to a method for real-time monitoring of the internal and external temperatures of a soft-pack lithium battery, which is applicable to the precise management of temperature fields and thermal safety control in fields such as power batteries and energy storage batteries. Background Art

[0002] With the rapid development of new energy vehicles and energy storage industries, the safety issues of lithium batteries have attracted increasing attention. As a key factor affecting the performance, life, and safety of lithium batteries, precise monitoring of temperature is crucial for the design of battery thermal management systems. However, there are still significant deficiencies in existing lithium battery temperature monitoring technologies, making it difficult to meet the stringent requirements for thermal safety of high-energy-density batteries.

[0003] Currently, lithium battery temperature monitoring mainly relies on surface-mounted thermocouples, infrared thermal imaging technology, or fiber optic sensing technology. Although surface-mounted thermocouples are easy to install, they can only obtain the surface temperature information of the battery and cannot reflect the internal temperature changes. Some studies have implanted thermocouples inside soft-pack batteries and used glass fiber to coat the thermocouples, which increases the volume of the sensor and thus affects the performance of the soft-pack battery. There are also studies that integrate thermal resistors on the current collector of the battery to monitor the internal temperature changes, but this integration method will have an irreversible impact on the service performance of the battery and it is difficult to ensure the reliability of the sensor in an electrolyte corrosive environment. Research shows that the internal thermal gradient of the battery is larger than the surface temperature difference, and traditional surface temperature measurement methods are prone to cause a lag in thermal runaway warnings. Although infrared thermal imaging technology can achieve non-contact temperature measurement, its spatial resolution is limited by the light transmittance of the battery packaging material and it cannot obtain the internal heat generation situation of the battery in a timely manner. In addition, fiber optic sensing technology has a high cost, the specific monitoring implementation process is complex, and fiber optic sensors are sensitive to multiple physical parameters (such as temperature, strain, stress, etc.), which may lead to signal cross-interference. For example, when an FBG sensor monitors temperature, it may also be affected by strain and stress, and complex signal decoupling and compensation are required. At the same time, due to the complex structure of fiber optic sensors, few studies have used such sensors to monitor the internal temperature changes of soft-pack batteries.

[0004] To obtain the internal temperature information of the battery, some studies have tried to implant sensors inside the battery. However, the existing implanted sensors usually have a diameter greater than 0.3 mm, and their physical size and material rigidity are likely to damage the integrity of the internal electrode group and separator of the battery, resulting in an increase in the capacity attenuation rate by 1%-5%.

[0005] On the other hand, existing temperature monitoring systems mostly adopt single-point or local temperature measurement methods and lack the ability to synchronously monitor the internal and external temperature fields of the battery. This limitation in data dimension makes it difficult for the battery thermal management system to establish an accurate three-dimensional thermal behavior model and unable to effectively predict the risks of local overheating or thermal runaway. Therefore, developing a high-precision, low-invasive, and multi-dimensional lithium battery temperature monitoring method has important theoretical significance and engineering value. Summary of the Invention

[0006] Aiming at problems in the prior art such as high invasiveness of sensors, lack of internal thermal field monitoring, and lag in dynamic response, the technical problem to be solved by the present invention is to provide a method for real-time monitoring of the internal and external temperatures of a soft-pack lithium battery, which can achieve accurate temperature monitoring while maximizing the maintenance of the original performance of the battery by optimizing the sensor layout strategy.

[0007] The technical solution adopted by the present invention to solve the above technical problem is as follows:

[0008] A method for real-time monitoring of the internal and external temperatures of a soft-pack lithium battery, the method comprising the following steps:

[0009] During the encapsulation process of the soft-pack battery, multiple ultra-fine thermocouples are implanted into key areas inside the battery to obtain the temperature change inside the battery; the key areas are: the area below the current collector, the position of the maximum thickness, and the area near the bottom of the casing;

[0010] At the same time, multiple distributed temperature measurement points are arranged on the outer surface of the battery, and ultra-fine thermocouples are respectively arranged to form a distributed monitoring network to obtain the temperature change outside the battery;

[0011] The temperature data is recorded in real time through a high-precision acquisition device, the sampling frequency is adjustable, and the temperature error does not exceed ±0.01°C.

[0012] The total volume of the implanted ultra-fine thermocouples accounts for less than 0.03% of the internal space of the battery.

[0013] Further, 3 ultra-fine thermocouples are respectively implanted at the horizontal center 5 mm below the current collector, the geometric center of the battery, and the horizontal center 5 mm above the bottom of the current collector, and the implantation depth is half of the thickness of the battery electrode group;

[0014] Five distributed temperature measurement points are arranged on the outer surface of the battery, symmetrically distributed at the center point and the four corners, and the temperature measurement points at the four corners are 8 mm away from the edge of the battery;

[0015] While achieving accurate temperature monitoring, the original performance of the battery is maximally maintained.

[0016] Further, the diameter of the ultra-fine thermocouple is ≤0.1 mm, and a double-layer self-healing insulation encapsulation process is adopted. The inner layer is a polyimide insulation layer resistant to electrolyte corrosion, and the outer layer is a polyurethane-siloxane copolymer elastomer coating with self-healing function. When microcracks occur on the sensor surface due to mechanical stress or the appearance of dendrites, the insulation layer can be self-healed through the dynamic recombination of molecular chains, ensuring that the sensor accuracy is not affected.

[0017] Further, the soft-pack lithium battery is a small soft-pack battery with a battery capacity of 1-5 Ah.

[0018] The process of the specific monitoring method is as follows:

[0019] 1) Encapsulate the ultra-fine thermocouple:

[0020] Uniformly coat a 5-nm-thick polyimide insulation layer on the surface of a T-type thermocouple with a diameter of 0.1 mm.

[0021] In a nitrogen environment, mix polyether polyol (PTMG-2000) and isocyanate (HDI) at a molar ratio of 1:1.3 and react at 70 °C for 3 hours; gradually add amino siloxane (KH-550, 8 wt%) and catalyst dibutyltin dilaurate (0.1 wt%), and continue to react for 1 hour to obtain a prepolymer; dissolve bis(2-hydroxyethyl) disulfide as a chain extender in N,N-dimethylformamide (DMF) and mix it with the prepolymer to obtain a polyurethane-siloxane copolymer.

[0022] Use an air spraying gun with a pressure of 0.3 MPa to spray a 40-50-μm-thick polyurethane-siloxane copolymer outside the polyimide insulation layer, pre-cure at 80 °C for 30 minutes, and cure at 120 °C for 60 minutes to form a flexible self-healing outer layer and obtain a complete encapsulation layer.

[0023] 2) Implant the ultra-fine thermocouple

[0024] Determine the key areas in the simulation software.

[0025] During the encapsulation process of the soft-pack battery, implant three of the above-encapsulated ultra-fine thermocouples inside the battery, which are located at TC1 5 mm below the horizontal center of the current collector, TC2 at the geometric center of the battery, and TC3 at the horizontal center above the bottom of the current collector respectively.

[0026] Arrange five thermocouples on the battery surface in a central point + four-corner symmetry manner. The thermocouple at the central point is denoted as TC6, and the thermocouples at the four corners are denoted as TC4, TC5, TC7, and TC8 respectively. The monitoring points at the four corners are 8 mm away from the battery edge.

[0027] Then perform battery encapsulation.

[0028] 3) Data acquisition

[0029] The encapsulated soft-pack battery is fixed on the battery test equipment by a fixture for charge and discharge cycle testing of the soft-pack battery; all thermocouples are electrically connected to the signal data acquisition and recorder for obtaining the monitoring data of all internal and external thermocouples arranged on the battery.

[0030] The signal data acquisition and recorder and the battery test equipment are both in communication with the host computer, and a dynamic temperature distribution map can be generated in the host computer, including the temperature difference between the inside and the surface, the temperature rise rate, and the change of the spatial thermal field, so as to realize the real-time monitoring of the internal and external temperatures.

[0031] The host computer is in communication with the data storage module for storing the collected or processed data.

[0032] Compared with the prior art, the advantages of the present invention are reflected in:

[0033] Low-invasive monitoring: The diameter of traditional implantable sensors is generally ≥0.3 mm, and after implantation, the battery capacity attenuation rate increases by 5%-8%. This application innovatively uses ultra-fine thermocouples with a diameter ≤0.1 mm, but its application faces two core problems: one is that ultra-fine T-type thermocouples are prone to breakage and signals are easily interfered, and the other is that the implantation process may cause electrolyte leakage or electrode damage. This application adopts a double-layer self-healing insulation encapsulation process, coating a corrosion-resistant polyimide insulation layer on the surface of the sensor to enhance mechanical strength and anti-interference; then spraying a polyurethane-siloxane copolymer elastomer coating with a self-healing function on the outer layer to prevent the sensor from failing due to the destruction of the corrosion-resistant insulation layer caused by the internal mechanical stress and the generation of lithium dendrites in the battery; implanting the thermocouple sensor during the battery assembly process to prevent electrolyte leakage or electrode damage. Verified by 1 / 3 / 5 Ah lithium iron phosphate / graphite battery experiments, after 100 cycles at 0.5C rate, the capacity attenuation rate only increases by 0.3%-1.1%. This monitoring method will not affect the normal operation of the battery.

[0034] Multi-point monitoring of the internal thermal field: Existing surface temperature measurement technologies, such as infrared thermal imaging, are limited by the battery shell occlusion and cannot obtain the internal temperature of the battery. By analyzing the structural characteristics and heat generation mechanism of lithium-ion batteries, this invention selects three internal monitoring points: the center 5 mm below the current collector (the ear-electrode connection interface), the geometric center of the battery (the position of the maximum thickness), and the center 5 mm at the bottom of the current collector (the area near the bottom of the shell), and implants 3 ultra-fine thermocouples to obtain the temperature change inside the battery. Multi-point temperature monitoring inside and outside solves the problems of poor accuracy of existing single-point measurement of internal temperature and incomplete temperature monitoring.

[0035] The method of the present invention can effectively monitor the temperature inside and outside the battery, and significantly improve the monitoring accuracy. After implanting the sensor, the open-circuit voltage deviation of the battery is <0.5%. In a constant temperature environment of 25±0.5°C, the sensor monitoring system can continuously and stably operate for more than 500 hours in an electrolyte corrosion environment, and the temperature drift error is <±0.2°C. It is proved that the influence of the monitoring method of the present invention on the electrochemical performance of small soft-pack batteries can be ignored when achieving high-precision detection.

[0036] This method realizes the high-precision synchronous perception of the internal and external temperature fields of soft-pack batteries. During the battery manufacturing process, the sensor is placed to ensure that the sensors can act together. The present invention uses a T-type ultra-fine thermocouple with a diameter ≤0.1 mm, combined with an insulation encapsulation process. While ensuring a monitoring accuracy of ±0.01°C, the capacity attenuation rate caused by implantation damage is reduced to less than 1.1%. By comparing the differences in temperature curves at different positions, this method quantifies the internal heat generation of the battery, providing data support and a new method for accurately obtaining the internal temperature change of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Schematic diagram of sensor arrangement: (a) Positions of internal thermocouples (5 mm below the center of the positive and negative electrode tabs (TC1), geometric center inside the battery (TC2), 5 mm above the bottom of the current collector (TC3)); (b) Positions of surface temperature-measuring thermocouples (TC4 - TC8, with 5 sensors distributed in an X shape).

[0038] Figure 2 Schematic diagram of the architecture of the battery temperature monitoring system used in the method of the present invention: It includes a number of sensors, a signal data acquisition recorder, a host computer (including analysis software) and battery test equipment.

[0039] Figure 3 Average capacity comparison chart of batteries with different capacities after 100 cycles of the battery.

[0040] Figure 4 Comparison curve of the highest internal and external temperatures of a 1Ah LFP battery at a high rate of 3C (10 cycles).

[0041] Figure 5 Comparison curve of the highest internal and external temperatures of a 5Ah LFP battery at a high rate of 3C (10 cycles).

[0042] Figure 6 Temperature distribution field map of the LFP battery established by COMSOL multi-physics simulation software (taking the single-layer positive and negative electrode lamination method as an example, the overall temperature distribution field of the small soft-pack battery is similar to the temperature distribution field of the single-layer positive and negative electrode lamination method). DETAILED DESCRIPTION OF THE INVENTION

[0043] The present invention will be further explained below in conjunction with embodiments and the accompanying drawings, but this is not intended to limit the scope of protection of this application.

[0044] A method for real-time monitoring of the internal and external temperatures of a soft-pack lithium battery. During the battery packaging stage, three ultra-fine T-type thermocouples with a diameter ≤ 0.1 mm are implanted into key internal areas (including the bottom of the current collector, near the tab, and the geometric center inside the battery), and five thermocouples are arranged on the battery surface to form a distributed monitoring network. The signal data acquisition recorder synchronously records the internal and external temperature changes, with a temperature detection accuracy of ±0.01 °C, and the total volume of the implanted sensors accounts for less than 0.03% of the internal space of the battery, avoiding substantial damage to the battery structure.

[0045] The signal data acquisition recorder supports multi-channel synchronous recording, and the temperature measurement accuracy reaches 0.01 °C.

[0046] Through comparative experiments to verify the impact of sensor implantation, the experimental group and the control group batteries are subjected to 100 charge and discharge cycles, charged to 3.65 V, and discharged to 2.5 V. The results show that the capacity attenuation of the experimental group is at most 1.1% more than that of the control group.

[0047] The temperature test is carried out in a constant temperature environment of 25 °C. For three types of batteries with capacities of 1 Ah, 3 Ah, and 5 Ah, they are charged and discharged at rates of 1C, 2C, and 3C respectively, and the internal and external temperature differences under different working conditions are recorded. The collected temperature data generates a dynamic temperature distribution map, including the temperature difference between the inside and the surface, the temperature rise rate, and the change of the spatial thermal field, and is transmitted to the data storage module in real time.

[0048] For the long-term stability test, during continuous monitoring for 500 hours, the drift error of the implanted sensor is less than ±0.2 °C, the capacity attenuation difference caused by sensor implantation is less than 1.1%, and the open-circuit voltage offset is less than 0.5%.

[0049] Embodiment

[0050] 1. Experimental system construction

[0051] In the experiment, three types of soft-pack lithium iron phosphate batteries with capacities of 1 Ah, 3 Ah, and 5 Ah are selected (the positive electrode is LiFePO4, and the negative electrode is graphite). The sizes of all batteries are 8*6 cm, which are small soft-pack batteries.

[0052] The double-layer packaging process is used to package the thermocouples in the experimental group:

[0053] A 5-nm-thick polyimide insulating layer is evenly coated on the surface of the T-type thermocouple with a diameter of 0.1 mm.

[0054] In a nitrogen environment, polyether polyol (PTMG-2000) and isocyanate (HDI) were mixed at a molar ratio of 1:1.3 and reacted at 70 °C for 3 hours. Amino silicone oil (KH-550, 8%) and the catalyst dibutyltin dilaurate (0.1 wt%, based on the mass ratio of the polyurethane-silicone copolymer) were added dropwise, and the reaction was continued for 1 hour to obtain a prepolymer. Bis(2-hydroxyethyl) disulfide was used as a chain extender and dissolved in N,N-dimethylformamide (DMF), and then mixed with the prepolymer to obtain a polyurethane-silicone copolymer.

[0055] Using an air spray gun (air pressure 0.3 MPa), a polyurethane-silicone copolymer elastomer with a thickness of about 50 μm was sprayed outside the polyimide layer, pre-cured at 80 °C for 30 minutes, and cured at 120 °C for 60 minutes to form a flexible self-healing outer layer; the integrity of the encapsulation layer was detected by microscopic imaging to ensure no bubbles or cracks.

[0056] During the encapsulation process of the experimental group batteries, 3 T-type thermocouples with a diameter of 0.1 mm were implanted inside the batteries. For the specific layout schematic diagram, see Figure 1 (a) in the figure, which are located at the horizontal center 5 mm below the positive electrode tab welding point (i.e., below the current collector) (TC1), the geometric center of the battery (TC2), and the center 5 mm above the bottom of the current collector TC3, that is, on the electrolyte / separator interface, and the three are on the same straight line. 5 thermocouples were arranged on the battery surface, as shown in Figure 1 (b) in the figure, distributed according to "center point (TC6) + four corner symmetric points (the thermocouples at the four corners are respectively denoted as TC4, TC5, TC7, and TC8)", and the monitoring points at the four corners are 8 mm away from the battery edge. The control group batteries maintained the original structure without implanting any sensors.

[0057] The monitoring system used in the method of this embodiment is as shown in Figure 2 The figure shows that the monitoring system includes sensors, a signal data acquisition recorder, a host computer, and battery test equipment. Among them, the battery test equipment (using a high-precision charge and discharge equipment CT-4008Tn-5V12A-204n (for low-rate working conditions) and CE-60004n-5V1200A-H (for high-rate working conditions)) performs the charge and discharge cycles of the battery, and the charge and discharge data is uploaded to the middle computer. Then, the signal data acquisition recorder (a multi-channel data acquisition device OHR-F800) obtains the temperature data measured by the internal and external sensors arranged on the battery. These parts together constitute the battery temperature monitoring system.

[0058] 2. Cyclic capacity control experiment

[0059] To evaluate the impact of sensor implantation on battery performance, charge-discharge cycle tests were conducted on the experimental group and the control group for 100 weeks. Charging was carried out at a constant current of 0.5C up to 3.65V, and discharging was at a constant current of 0.5C down to 2.5V. As Figure 3 shown, after 100 cycles, the average capacity retention rates of the batteries in the experimental group were: 98.7% for the 1Ah battery, 97.9% for the 3Ah battery, and 96.5% for the 5Ah battery. The maximum increase in average capacity decay compared to the control group was only 1.1% (for the 5Ah battery), indicating that the impact of sensor implantation on electrochemical performance is negligible.

[0060] 3. Multi-rate temperature monitoring experiment

[0061] In a constant temperature environment, stepwise charge-discharge tests were conducted on the batteries in the experimental group to focus on the temperature field distribution characteristics under different capacity / rate combinations. The experiment covered three typical working conditions of 1C, 2C, and 3C (specific current values: 1A / 2A / 3A for the 1Ah battery, and 5A / 10A / 15A for the 5Ah battery). Each group of tests was carried out for 10 charge-discharge cycles to ensure data repeatability.

[0062] 3.1 Low-rate working condition (1C)

[0063] During the constant current discharge process of the 1Ah battery at 1C, the internal temperature measurement point 2 (the geometric center inside the battery (TC2)) had the highest temperature, with a recorded peak temperature of 26.34°C. The surface center point (TC6) had the highest temperature, with a peak temperature of 26.16°C, and the internal-external temperature difference was only 0.18°C. At this time, the temperature field distribution was relatively uniform (standard deviation < 0.5°C), indicating that the internal heat generation rate of the battery was basically balanced with the surface heat dissipation under low current conditions.

[0064] 3.2 Medium and high-rate working conditions (2C - 3C)

[0065] When the discharge rate was increased to 3C, the internal temperature measurement point 1 (5mm below the center of the positive and negative electrode tabs, TC1) of the 1Ah battery had the highest temperature, and the temperature rapidly rose to 27.74°C ± 0.15°C during the discharge stage. The peak temperature of the surface temperature measurement point was 27.44°C, and the internal-external temperature difference expanded to 0.30°C (as Figure 4 shown in the temperature-time curve). It should be noted that in the middle and late stages of discharge (SOC: 30% - 10%), the internal temperature rise rate showed a significant steep increase, which may be related to the accumulation of Joule heat caused by the aggravation of concentration polarization.

[0066] The test on the 5Ah battery further revealed the impact of capacity size on battery temperature: under the 3C discharge working condition, the internal electrolyte interface temperature measurement point 3 had the highest temperature, with a peak temperature reaching 33.85°C, which was 1.76°C higher than the highest surface temperature (32.09°C), as Figure 5The experimental data show that when the battery capacity increases, the internal heat accumulation effect shows a nonlinear growth trend.

[0067] Although the critical point of thermal runaway was not triggered under the experimental conditions, the monitoring data has revealed potential risks: at the end of 3C discharge, the internal temperature of a 5Ah battery is close to 34°C. If it continues to operate or encounters poor heat dissipation, it may trigger a chain of exothermic reactions (such as SEI film decomposition, electrolyte oxidation, etc.). Therefore, real-time monitoring of internal temperature has important engineering value for early warning of safety hazards such as electrolyte failure and gas generation.

[0068] 3.3 Long-term stability test

[0069] Long-term stability testing observed the changes in the sensor when it was implanted in the battery. During 500 hours of continuous monitoring, the sensor drift error was less than ±0.2°C, the capacity attenuation difference caused by sensor implantation was <1.1%, and the open circuit voltage offset was <0.5%.

[0070] The present invention uses a T-type thermocouple temperature measuring line with a smaller volume and relatively higher accuracy to monitor the temperature of multiple points inside and outside the soft-pack lithium battery, and the heat generation conditions at different positions of the soft-pack battery are reflected through the measured temperature changes. At the same time, the T-type thermocouple sensor selected by the present invention has a certain flexibility. This feature can minimize the problem of battery performance being affected by the volume occupied by the sensor. In addition, traditional packaging materials are prone to damage to the insulating layer due to electrolyte erosion or mechanical stress during long-term circulation, causing signal drift or short circuit risks. The present invention uses a double-layer self-healing packaging setting, the inner layer of polyimide provides basic corrosion resistance, and the outer layer of polyurethane-siloxane copolymer elastomer achieves self-repair through dynamic cross-linking of molecular chains when slightly damaged, making it possible for it to be used long-term inside the battery.

[0071] Any matters not described in the present invention are applicable to the prior art.

Claims

1. A method for real-time monitoring of the internal and external temperatures of a soft-pack lithium battery, characterized in that, The method includes the following steps: During the packaging process of the soft-pack battery, multiple ultra-fine thermocouples are implanted into key areas inside the battery to obtain the temperature changes inside the battery; the key areas are: the area below the current collector, the position of the maximum thickness, and the area near the bottom of the casing; At the same time, multiple distributed temperature measurement points are set on the outer surface of the battery, and ultra-fine thermocouples are respectively arranged to form a distributed monitoring network to obtain the temperature changes outside the battery; And the total volume of the implanted ultra-fine thermocouples accounts for less than 0.03% of the internal space of the battery; <0.03% The temperature data is recorded in real time by a high-precision acquisition device, the sampling frequency is adjustable, and the temperature error does not exceed ±0.01°C.

2. The monitoring method according to claim 1, characterized in that Three ultra-fine thermocouples are respectively implanted at the horizontal center 5 mm below the current collector, the geometric center of the battery, and the horizontal center 5 mm above the bottom of the current collector, and the implantation depth is half of the thickness of the battery electrode group; Five distributed temperature measurement points are arranged on the outer surface of the battery, symmetrically distributed according to the center point and the four corners, and the temperature measurement points at the four corners are 8 mm away from the edge of the battery; While realizing accurate temperature monitoring, the original performance of the battery is maintained to the greatest extent.

3. The monitoring method according to claim 1, wherein The diameter of the ultra-fine thermocouple is ≤0.1 mm, and a double-layer self-healing insulation packaging process is adopted. The inner layer is a polyimide insulation layer resistant to electrolyte corrosion, and the outer layer is a polyurethane-siloxane copolymer elastomer coating with self-healing function. When micro-cracks appear on the surface of the sensor due to mechanical stress or dendrites, the insulation layer can be self-healed through the dynamic recombination of molecular chains to ensure that the sensor accuracy is not affected.

4. The monitoring method according to claim 1, characterized in that, The soft-pack lithium battery is a small soft-pack battery, and the battery capacity is 1-5 Ah.

5. A method for real-time monitoring of the internal and external temperatures of a soft-pack lithium battery, characterized in that, The process of the monitoring method is as follows: 1) Packaging the ultra-fine thermocouple: A 5-nm-thick polyimide insulation layer is evenly coated on the surface of a T-type thermocouple with a diameter of 0.1 mm; In a nitrogen environment, polyether polyol (PTMG-2000) and isocyanate (HDI) are mixed at a molar ratio of 1:1.3 and reacted at 70°C for 3 hours; amino siloxane (KH-550, 8 wt%) and catalyst dibutyltin dilaurate (0.1 wt%) are added dropwise and the reaction is continued for 1 hour to obtain a prepolymer; bis(2-hydroxyethyl) disulfide is used as a chain extender and dissolved in N,N-dimethylformamide (DMF) and mixed with the prepolymer to obtain a polyurethane-siloxane copolymer; Using an air spraying gun with an air pressure of 0.3 MPa, a 40-50-μm-thick polyurethane-siloxane copolymer is sprayed outside the polyimide insulation layer, pre-cured at 80°C for 30 minutes, and cured at 120°C for 60 minutes to form a flexible self-healing outer layer, obtaining an integral packaging layer; 2) Implanting the ultra-fine thermocouple During the packaging process of the soft-pack battery, three above-packaged ultra-fine thermocouples are implanted inside the battery, which are located at TC1 at the horizontal center 5 mm below the current collector, TC2 at the geometric center of the battery, and TC3 at the horizontal center 5 mm above the bottom of the current collector; Five thermocouples are arranged on the battery surface in a center point + four-corner symmetry manner. The thermocouple at the center point is denoted as TC6, and the thermocouples at the four corners are respectively denoted as TC4, TC5, TC7, and TC8. The monitoring points at the four corners are 8 mm away from the edge of the battery; Then the battery is packaged; 3) Data acquisition The encapsulated pouch cell is fixed on the battery test equipment by a fixture for performing charge and discharge cycle tests on the pouch cell; all thermocouples are electrically connected to the signal data acquisition and recording instrument for obtaining the monitoring data of all internal and external thermocouples arranged on the battery. The signal data acquisition and recording instrument and the battery test equipment are both in communication with the host computer, and a dynamic temperature distribution map can be generated in the host computer, including the temperature difference between the inside and the surface, the temperature rise rate, and the change of the spatial thermal field, so as to realize the real-time monitoring of the internal and external temperatures. The host computer is in communication with the data storage module for storing the collected or processed data.

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