Lithium battery temperature change thermal parameter measuring method and device

Abstract

The invention belongs to the technical field of new energy lithium battery measurement, and particularly relates to a lithium battery temperature change thermal parameter measurement method and device. Under the condition of considering the heat loss, the specific heat capacity and the anisotropic heat conductivity coefficient of the lithium battery under the temperature change can be synchronously measured through a single experiment, and the test efficiency and the measurement precision are greatly improved. The device is suitable for cylindrical, square, soft package and blade lithium batteries, can perform measurement under various different equivalent heat exchange boundary conditions including air natural convection, heat insulation material wrapping, vacuum, heat insulation calorimeters and the like, is convenient to operate, high in accuracy and high in adaptability, can realize rapid and accurate measurement of thermal parameters of the lithium batteries at different temperatures, and is suitable for popularization and application. And high efficiency and high precision are both considered.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy lithium battery measurement, and in particular relates to a method and device for measuring temperature-dependent thermal parameters of a lithium battery. Background Art

[0002] In recent years, electric vehicles have played an important role in alleviating energy crises and environmental pollution. Lithium-ion batteries have the advantages of high energy density, long life, and low self-discharge rate, making them the preferred power source for electric vehicles.

[0003] However, the characteristics of lithium-ion batteries are closely related to operating temperature. When the battery temperature reaches a high threshold, the solid electrolyte interface layer decomposes, or worse, leads to thermal runaway with smoke, fire, or explosion. Conversely, low temperatures increase internal resistance, leading to a sharp decline in battery discharge capacity and electric vehicle performance. Clearly, the safety of lithium-ion battery thermal management has become a critical issue in the development of electric vehicles. Thermal parameters are essential for modeling, simulating, and controlling battery thermal management systems. In-depth research on lithium-ion battery thermal parameters is essential for accurately predicting battery temperature changes, improving battery performance, extending battery life, and even suppressing and eliminating thermal runaway hazards. This research holds significant scientific significance and practical application value.

[0004] It should be noted that the thermal conductivity of lithium batteries is anisotropic, and both the thermal conductivity and specific heat capacity change with temperature. Therefore, in lithium battery testing and research, it is particularly important to measure the thermal parameters under temperature changes. The thermal parameters under temperature changes can better reflect the actual state of lithium batteries in actual applications.

[0005] The thermal parameter measurement methods for lithium batteries are mainly divided into steady-state and transient methods. The steady-state method establishes a stable temperature gradient field and uses Fourier's law of heat conduction for measurement. Its measurement results have high accuracy and reliability, but the test process is relatively complex and it takes a long time to reach thermal equilibrium. The transient law is based on the theory of non-steady-state heat transfer. It calculates the thermal conductivity by monitoring the temperature change characteristics of the sample over time. It has the advantages of short test time and convenient operation, but the reliability of its results is slightly insufficient compared to the steady-state method. The quasi-steady-state method is between the steady-state method and the transient method. This method uses the thermal response characteristics of the system in the process of forming a steady state. When the temperature rise rate at each position inside the sample is approximately the same, more accurate measurement results can be obtained in a shorter test time. This method not only retains the high reliability characteristics of the steady-state method, but also significantly shortens the test cycle, and has high practical value in engineering applications.

[0006] The establishment of a quasi-steady state requires certain adiabatic boundary conditions. Existing quasi-steady state methods include adiabatic quasi-steady state measurement and calibration calorimetry. However, these two test methods have the following problems:

[0007] (1) The quasi-steady-state method can only perform a single measurement. When measuring at variable temperatures, the experimental measurement efficiency is low, and it is necessary to set different initial ambient temperatures to perform variable temperature measurements.

[0008] (2) When the quasi-steady-state method is used to measure the thermal conductivity of lithium batteries, a single experiment can only measure the thermal conductivity in one direction, which is not convenient for efficiently measuring the anisotropic thermal conductivity of lithium batteries.

[0009] (3) Adiabatic quasi-steady-state measurement method: In order to ensure that the battery is tested under adiabatic boundary conditions, it is necessary to evacuate the battery or set adiabatic boundary conditions for processing. The process is tedious and the operation is complicated. In fact, it is difficult to meet the requirements of ideal adiabatic boundary conditions, which affects the accuracy of the measurement results.

[0010] (4) The calibration calorimetry method involves wrapping lithium batteries with insulation materials in the early stages. This requires measuring both the temperature rise and temperature drop of the lithium battery. The heat loss during the temperature rise process is calculated through the temperature drop process, and then the thermal conductivity and specific heat capacity of the lithium battery are calculated. This significantly increases the test time and cost, with the test process lasting up to 3-4 hours per temperature stage. The heat loss during the temperature rise and temperature drop processes is not completely consistent, and the specific heat capacity measurement error for smaller samples will be relatively large.

[0011] (5) Both the adiabatic quasi-steady-state measurement method and the calibrated calorimetry method require the lithium battery to be wrapped with insulating materials. Without a specific device for wrapping and packaging, the degree of wrapping in each experiment will be different, which will affect the accuracy of the measurement. Summary of the Invention

[0012] In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to provide a method and device for measuring the temperature-dependent thermal parameters of a lithium battery.

[0013] In order to achieve the above objectives, a first aspect of the present invention provides a method for measuring thermal parameters of a lithium battery, comprising:

[0014] S1: Construct a composite thermal conductive test structure on the end face of the lithium battery and use a fixture to encapsulate it.

[0015] S2: Place the packaged battery fixture in a precision constant temperature and humidity chamber, connect the heating and temperature measuring equipment, stabilize the initial ambient temperature, and eliminate ambient temperature disturbances.

[0016] S3: Apply constant power for directional heating, and continue heating until the lithium battery temperature reaches the required upper temperature limit, and simultaneously collect dynamic temperature rise data on all directions.

[0017] S4: Calibrate the equivalent additional heat capacity by measuring the high-purity titanium standard sample to determine the additional heat capacity value of the fixture.

[0018] S5: Obtain the energy conservation equation for one-dimensional heat conduction considering heat loss, and measure the specific heat capacity and thermal conductivity of lithium batteries under temperature changes through quasi-synchronous temperature rise curves and model multi-parameter identification.

[0019] A second aspect of the present invention provides a device for implementing the above-mentioned method for measuring the temperature-dependent thermal parameters of a lithium battery. The device adopts a modular design and mainly includes the following core functional modules:

[0020] Constant power excitation module: uses a high-precision regulated DC power supply system to achieve constant power output to the heating film, ensuring a uniform heat flux density field on the surface of the lithium battery and achieving controllable quasi-synchronous temperature rise conditions.

[0021] Data acquisition module: Integrates a high-resolution thermocouple temperature measurement system (accuracy up to ±0.1°C), is equipped with a multi-channel data acquisition card and anti-interference shielding technology, and enables real-time and accurate monitoring and data recording of lithium battery temperature.

[0022] Sample Encapsulation Module: A custom encapsulation fixture is designed for the shape of lithium batteries. The use of aerogel insulation significantly reduces heat loss during the experiment. The fixture is easy to operate and can encapsulate batteries of varying sizes.

[0023] Environmental control module: uses a programmable precision constant temperature and humidity chamber to provide ±0.1°C temperature control accuracy and ±2%RH humidity stability, establishing ideal thermodynamic boundary conditions for lithium batteries and effectively isolating environmental disturbances.

[0024] In general, compared with the prior art, the present invention has the following significant advantages:

[0025] 1. While taking heat loss into account, the present invention can simultaneously measure the specific heat capacity and anisotropic thermal conductivity of lithium batteries under temperature changes in a single experiment, greatly improving test efficiency and measurement accuracy.

[0026] 2. The present invention is applicable to cylindrical, square, soft-pack and blade lithium batteries, and can be measured under a variety of equivalent heat exchange boundary conditions, including natural air convection, insulation material wrapping, vacuum, adiabatic calorimeter, etc. It is easy to operate, highly accurate, and highly adaptable. It can realize the rapid and accurate measurement of the thermal parameters of lithium batteries at different temperatures, taking into account both high efficiency and high precision.

[0027] 3. This invention adaptively identifies heat loss parameters during measurement without requiring complex lithium battery processing, significantly improving measurement repeatability and stability. Furthermore, it supports multi-channel automated measurement, enabling continuous measurement of temperature-dependent thermal parameters across multiple samples, meeting high-volume testing requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a flow chart of a method for measuring temperature-dependent thermal parameters of a lithium battery according to an embodiment of the present application.

[0029] Figure 2 This is a thermocouple distribution diagram of an embodiment of the present application.

[0030] Figure 3 This is a schematic diagram of quasi-one-dimensional heat flow distribution in heat conduction in an embodiment of the present application.

[0031] Figure 4 This is a simulated quasi-synchronous temperature rise diagram in the lithium battery measurement experiment of the embodiment of the present application.

[0032] Figure 5 This is a simplified schematic diagram of measuring a lithium battery under various equivalent heat exchange boundary conditions according to an embodiment of the present application.

[0033] Figure 6 This is a schematic diagram of the device structure of the first embodiment of the present application.

[0034] Figure 7 This is a schematic diagram of the device structure of the second application embodiment of the present application.

[0035] Figure 8 This is a graph of the temperature rise and temperature rise rate of a standard sample of pure titanium measured in an embodiment of the present application.

[0036] Figure 9 This is a graph showing the thermal conductivity results of cylindrical lithium batteries of different models measured in Example 1 of the present application.

[0037] Figure 10 This is a graph showing the specific heat capacity of cylindrical lithium batteries of different models measured in Example 1 of the present application.

[0038] Figure 11 This is a graph showing the trend of thermal conductivity changes of square lithium batteries of different brands measured in Example 2 of the present application.

[0039] Figure 12 This is a graph showing the trend of thermal conductivity changes of square lithium batteries measured using the second embodiment of the present application.

[0040] Figure numerals: 1. Thermocouple, 2. Round copper sheet, 3. Round thermal conductive silicon pad, 4. Cylindrical lithium battery, 5. Round polyimide heating film, 6. Locking device, 7. Teflon clamp, 8. Cylindrical clamp aerogel insulation material, 9. Cylindrical clamp slide rod pushing device, 10. Square polyimide heating film, 11. Square thermal conductive silicon pad, 12. Square lithium battery, 13. Square copper sheet, 14. Metal aluminum plate, 15. Square clamp aerogel insulation material, 16. Square clamp slide rod pushing device. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the described embodiments are only used to conclude the present invention and are not intended to limit the present invention.

[0042] This application provides a method and device for measuring the thermal parameters of lithium batteries with short testing times, accurate results, a wide range of applications, low testing costs, and ease of implementation. In a single experiment, the device can simultaneously measure the anisotropic thermal conductivity and temperature-dependent specific heat capacity of lithium batteries at different temperatures. This method provides important data and methodological support for optimizing the design of battery thermal management systems. It is recommended that anisotropic thermal conductivity measurements be performed on batteries in actual engineering applications, allowing for optimization of battery thermal management strategies based on actual parameters.

[0043] like Figure 1 As shown, the embodiment of the present application provides a method for measuring temperature-dependent thermal parameters of a lithium battery, comprising:

[0044] S1: Construct a composite thermal conductive test structure on the end face of the lithium battery and encapsulate it with a special fixture with aerogel wrapping material inside.

[0045] For prismatic, soft-pack, and blade-shaped lithium batteries, the composite thermal conductivity test structure is constructed by arranging the thermal conductive silicon pad, copper sheet, and thermal conductive silicon pad in the order of "thermal conductive silicon pad" on the bottom of the lithium battery; then arranging the same order on the top of the lithium battery, and then adding a heating film in contact with the copper sheet for uniform heat distribution. For cylindrical lithium batteries, the composite thermal conductivity test structure is constructed by arranging the thermal conductive silicon pad and copper sheet on the positive end of the lithium battery; then symmetrically arranging the thermal conductive silicon pad and copper sheet on the negative end of the lithium battery, and then contacting the heating film with the copper sheet for uniform heat distribution.

[0046] like Figure 2 As shown, in order to prevent the heating film from interfering with the temperature measurement, a thermocouple 1 is embedded in the copper sheet to collect temperature data in real time during the temperature rise process. For square, soft-pack and blade lithium batteries, the embedding positions of the thermocouple 1 include: the center point of the top, the center point of the upper long side, the center point of the upper wide side and the center point of the bottom. For cylindrical lithium batteries, the embedding positions of the thermocouple 1 include: the center point of the positive terminal surface, the center point of the negative terminal surface, any point on the boundary of the positive terminal surface and any point on the boundary of the negative terminal surface; wherein, any point on the boundary of the positive terminal surface and any point on the boundary of the negative terminal surface are symmetrical in the vertical direction.

[0047] It should be noted that cracks must be avoided when the lithium battery is in contact with the thermally conductive silicon pad, copper sheet, and heating sheet to avoid introducing additional thermal resistance and affecting the test results.

[0048] S2: Place the packaged battery fixture in a precision constant temperature and humidity chamber, connect the heating and temperature measuring equipment, stabilize the initial ambient temperature, and eliminate ambient temperature disturbances.

[0049] S3: Apply constant power for directional heating and continue heating until the lithium battery temperature reaches the required upper temperature limit, and simultaneously collect dynamic temperature rise data of the end face.

[0050] It's important to maintain a constant heating power to ensure the lithium-ion battery continues to heat up. 500 seconds after the test begins, the system enters a quasi-synchronous temperature rise state, where the temperature rise rate at each cross-section of the battery converges to a consistent level. Testing continues until the battery reaches the target temperature. Thermal parameters at different temperatures are calculated based on test data from different time intervals.

[0051] S4: Calibrate the additional heat capacity by measuring the high-purity titanium standard sample to determine the additional heat capacity value of the fixture.

[0052] It is important to note that the additional heat capacity must be calibrated using a high-purity titanium standard sample. This calibration process only needs to be performed once to determine the additional heat capacity value, facilitating the subsequent accurate measurement of lithium-ion battery thermal parameters under different state of charge (SOC) conditions.

[0053] S5: Obtain the energy conservation equation for one-dimensional heat conduction considering heat loss, and measure the specific heat capacity and anisotropic thermal conductivity of lithium batteries under temperature changes through quasi-synchronous temperature rise curves and model multi-parameter identification.

[0054] Furthermore, the S5 is specifically as follows:

[0055] S51: Obtain the energy conservation equation for one-dimensional heat conduction considering heat loss, as well as the temperature rise rate at both end surfaces of the battery and the ambient temperature set in the constant temperature and humidity chamber.

[0056] The energy conservation equation is:

[0057]

[0058] in is a constant heat flux density, that is, a constant power per unit area provided by a constant voltage and constant current source. S represents the cross-sectional area of ​​the lithium battery heating surface. and are the mass and equivalent specific heat capacity of the lithium battery, Indicates any spatial position in the lithium battery, Indicates the ambient temperature, is the overall equivalent heat transfer coefficient of the lithium battery surface. This formula establishes the dynamic relationship of battery thermal balance, indicating that the input of lithium battery It is mainly used for two parts: the thermal capacity effect of the battery itself and the heat convection loss on the surface of the lithium battery.

[0059] S52: Performing a quasi-synchronous temperature rise parameter identification method on the energy conservation equation to obtain an equivalent heat transfer coefficient of the entire fixture and a specific heat capacity of the lithium battery.

[0060] It's important to note that during heat transfer, which involves heat loss, the entire fixture isn't a perfectly adiabatic boundary. Temperature measurements must be taken at multiple locations across the lithium battery to determine whether the temperature rise rate is consistent across all sections, ensuring a quasi-synchronous temperature rise. Data testing revealed that the temperature rise rate deviation between sections was less than 0.3%, confirming a quasi-synchronous temperature rise.

[0061] According to the characteristics of quasi-synchronous temperature rise, the temperature rise rate of any cross section in the lithium battery is consistent: , and Represent any two cross-sectional positions in the battery. Perform time integration and global equivalent processing on the energy conservation equation:

[0062]

[0063] in and Indicates the starting point and measurement end point of the lithium battery entering the quasi-synchronous temperature rise. represents a constant term, Represents the total surface area of ​​a lithium battery.

[0064] It should be noted that the fitting results in an equation for the three-dimensional function: , and are the coefficients of the three-dimensional functional equation, Is a constant. The equivalent specific heat capacity of lithium battery , equivalent heat transfer coefficient .

[0065] Due to the existence of additional heat capacity, calibration is required. The additional heat capacity calibration is performed using the standard sample high-purity titanium. The calibration result is the specific heat capacity c of the lithium battery. li .

[0066] The measurement results are shown in Table 1.

[0067] Table 1 Measurement results of standard sample pure titanium

[0068]

[0069] S53: The equivalent heat transfer coefficient obtained Substitute the thermal conductivity calculation formula that takes heat loss into account to obtain the thermal conductivity of the lithium battery:

[0070]

[0071] in is the path length in the direction of heat conduction, Indicates the cross-sectional area of ​​the lithium battery heating surface, is the temperature difference between the two ends of the lithium battery.

[0072] and is the heat flow in and out of the two ends of the lithium battery, which can be expressed as:

[0073]

[0074]

[0075] in is the temperature of the lithium battery heating end, is the temperature of the cold end of the lithium battery, and the equivalent heat transfer coefficient is obtained Substituting this into the equation, we can calculate the anisotropic thermal conductivity of the lithium battery.

[0076] It should be noted that in the heat transfer process based on heat loss, heat conduction is quasi-one-dimensional heat transfer. Considering the heat flow of heat loss on the side of the lithium battery, it is equivalent to a vector. There is an angle between the heat flow conducted in the axial direction and the heat loss heat flow on the side. .like Figure 3 shown.

[0077] Furthermore, the heat flux density Subtracting the heat loss from the heat flux can give the axial heat flux flowing through the cylindrical lithium battery. Substituting this into the thermal conductivity calculation formula that takes heat loss into account, the axial thermal conductivity of the cylindrical lithium battery can be obtained:

[0078]

[0079] in is the axial heat flux, is the length of the cylindrical lithium battery, is the temperature difference between the two ends of the cylindrical lithium battery in the height direction, is the bottom area of ​​the cylindrical lithium battery.

[0080] like Figure 3 As shown, there is an angle between the axial heat flow and the lateral heat loss heat flow. , subtract the heat absorbed by the battery itself from the heat flow in the axial direction, and then calculate the vector angle to obtain the heat flow in the radial direction. Substituting the above results into the thermal conductivity calculation formula considering heat loss, the radial thermal conductivity calculation formula can be obtained:

[0081]

[0082] in is the radial thermal conductivity of cylindrical lithium batteries, is the radius of the cylindrical lithium battery, It is the difference between the average temperature of the upper and lower ends and the average temperature of the two sides. is the lateral area of ​​cylindrical lithium battery, .

[0083] Furthermore, the anisotropic thermal conductivity of square, soft-pack and blade lithium batteries is divided into three directions: length, height and thickness. By giving a constant heat flux density in the length direction , so that the temperature of the lithium battery rises. The equivalent heat transfer coefficient obtained by fitting Multiply the corresponding cross-sectional area and the temperature difference at both ends to obtain the heat flow of heat loss. Substitute the difference between the heat flow in the longitudinal direction and the heat flow of heat loss into the thermal conductivity calculation formula that takes heat loss into account to obtain the thermal conductivity calculation formula in the longitudinal direction:

[0084]

[0085] Similarly, there is an angle between the heat flow in the length direction and the heat flow in the height and thickness directions. and The vector angle between the heat flow in the length direction and the heat absorbed by the battery is calculated and substituted into the thermal conductivity calculation formula that takes heat loss into account to obtain the thermal conductivity calculation formula in the height direction and thickness direction:

[0086]

[0087]

[0088] in They are the length, height and thickness of square, soft-pack and blade lithium batteries respectively. is the path of heat conduction, yes The heat flux density in the direction is , and S is the cross-sectional area. , .

[0089] This method for measuring the temperature-dependent thermal parameters of lithium batteries can simultaneously measure the anisotropic thermal conductivity and temperature-dependent specific heat capacity of lithium batteries in a single experiment. It is suitable for measuring various types of lithium batteries and does not require complex processing of the lithium batteries. It can adaptively identify heat loss parameters during the measurement process, significantly improving the repeatability and stability of the measurement.

[0090] like Figure 3 As shown in the figure, this figure is a schematic diagram of the heat transfer direction distribution of heat flow in the heat transfer process based on heat loss.

[0091] like Figure 4 As shown in the figure, this is a quasi-synchronous temperature rise diagram of the simulation experiment. Under the scenario of small equivalent heat transfer coefficient, a constant heat flux is applied. After heating for 500s, the entire system enters a quasi-synchronous temperature rise state. 、 、 、 The corresponding equivalent heat transfer coefficients calculated by the quasi-synchronous temperature rise parameter identification method for the curves of the four stages can be used to calculate the specific heat capacity and anisotropic thermal conductivity at different temperatures.

[0092] Figure 5 The following are simplified schematic diagrams of lithium battery measurements under various equivalent heat exchange boundary conditions, as shown in the examples of the present application. (a) illustrates testing under natural air convection, (b) under vacuum, and (c) within an adiabatic calorimeter. The battery does not require wrapping. Instead, a polyimide heating film is placed on one end of the battery to provide a constant heat source. Thermocouples are placed at both ends of the battery to measure temperature in real time. The battery is then placed in the test environment for measurement, and its thermal parameters can be calculated using parameter identification methods.

[0093] Furthermore, different boundary conditions will affect measurement accuracy and convenience:

[0094] (1) Natural convection air does not require insulation treatment and is easy to operate. However, the equivalent heat transfer coefficient of natural convection air is about 10-15 In principle, it will affect the consistency of quasi-synchronous temperature rise, thus affecting the measurement accuracy. The measurement accuracy of thermal conductivity and specific heat capacity is about 5%. Through heat transfer coefficient calibration, the measurement accuracy can be reduced to within 3%.

[0095] (2) Vacuum can effectively achieve quasi-steady-state conditions that are closer to the adiabatic boundary, but the experimental setup and operation under vacuum need to consider more, such as the contact thermal resistance under vacuum, and the measurement requirements are high. The connecting wires, heating films, and thermocouples will also introduce additional heat capacity. Through heat transfer coefficient calibration, the measurement accuracy can be achieved within 3%.

[0096] (3) The adiabatic calorimeter uses adiabatic tracking to obtain a relatively adiabatic environment, but in essence it still uses air for adiabatic treatment. The high-temperature end face and the low-temperature end face of the battery exchange heat through the air. The thermal conductivity measurement results will have some deviations, and the measurement accuracy is within 3%.

[0097] It should be noted that the equivalent heat transfer coefficient of the insulation material wrapping method is between 2-10 However, it will introduce additional system heat capacity and needs to be calibrated through heat transfer coefficient and standard samples. The measurement accuracy can be within 2%.

[0098] Application Example 1: Thermal Parameter Measurement of Cylindrical Lithium Batteries

[0099] This application example uses Panasonic 21700 cylindrical lithium battery with a capacity of 5Ah and a mass of 65.8g. Figure 6 In (a), a circular thermal conductive silicon pad 3 and a circular copper sheet 2 are placed on the negative end surface of the cylindrical lithium battery 4, and a circular polyimide heating film 5 is placed in contact with the copper sheet for uniform heating; a circular thermal conductive silicon pad 3 and a circular copper sheet 2 are symmetrically arranged on the positive end surface. The arrangement result is shown in FIG. Figure 6 As shown in (b).

[0100] To ensure the uniformity of the experimental boundary conditions, a special fixture is used to package the cylindrical lithium battery, such as Figure 6 As shown in (d), the encapsulated battery fixture is placed in a high-precision constant temperature chamber to monitor battery temperature changes. Once thermal equilibrium is reached, a DC power supply provides constant power input to the heating module, stimulating the lithium battery to heat up.

[0101] During this process, a temperature difference is generated at the positive and negative ends of the battery, which is specifically manifested as ,in and The temperature at the positive and negative electrode ends, respectively, is a temperature gradient. This temperature gradient causes heat conduction within the battery, with the heat flow directed from the high-temperature area to the low-temperature area. This quasi-synchronous temperature rise parameter identification measurement method can be used to calculate the thermal parameters of cylindrical lithium batteries.

[0102] It should be noted that in order to better reduce the test error, this application example 1 provides a capsule-shaped fixture. Figure 6 As shown in (c), the outer layer of the fixture is composed of a Teflon fixture 7, and the inner layer is filled with a cylindrical fixture aerogel insulation material 8. The side is locked by a locking device 6 to make the wrapping material in close contact with the side of the lithium battery, and the end face is pushed by a cylindrical fixture slide rod pushing device 9 to make the aerogel insulation material in close contact with both ends of the lithium battery, thereby minimizing heat loss and reducing the equivalent heat transfer coefficient to meet the boundary conditions of quasi-synchronous temperature rise.

[0103] This fixture is suitable for measuring cylindrical lithium batteries of any size. By stacking the fixtures, any number of cylindrical lithium batteries can be measured without having to customize the mold based on the size of the cylindrical lithium battery. This reduces the test cost and greatly improves the efficiency of the experiment. By continuously heating to obtain quasi-synchronous temperature rise curves at different temperature stages and changing the battery's state of charge, thermal parameters can be obtained at different temperatures and SOC states.

[0104] Application Example 2: Thermal Parameter Measurement of Prismatic, Soft-Pack, and Blade Lithium Batteries

[0105] This application example uses a square hard-shell lithium battery with a size of , its capacity is 32Ah and its mass is 764.7g. Figure 7 As shown in (a), a square thermal conductive silicon pad 11 and a square copper sheet 13 are placed on the top of the square lithium battery 12, and then a square polyimide heating film 10 is added to contact the copper sheet for uniform heating; a square thermal conductive silicon pad 11 and a square copper sheet 13 are also symmetrically arranged below, and then the processed square lithium battery is placed in a special fixture, as shown in FIG. Figure 7 As shown in (b), the packaged battery fixture is placed in a high-precision constant temperature chamber to monitor battery temperature changes. Once thermal equilibrium is reached, a DC power supply provides constant power input to the heating film, stimulating the lithium battery to heat up.

[0106] During this process, a temperature difference is generated between the upper and lower surfaces of the square lithium battery, which is specifically manifested as ,in and The temperatures of the heated end face and the symmetrical end face, respectively. This temperature gradient causes heat conduction within the battery, with the heat flow directed from the high-temperature area to the low-temperature area. This quasi-synchronous temperature rise parameter identification measurement method can be used to calculate the thermal parameters of prismatic lithium batteries.

[0107] like Figure 7 As shown in (c), in order to ensure the uniformity of the experimental boundary conditions, the outer layer of the fixture is a metal aluminum plate 14, and the inner layer is provided with a 20mm thick square fixture aerogel insulation material 15 on the upper and lower surfaces in contact with the battery, and its thermal conductivity is 0.02 The surrounding area is also made of 20mm thick aerogel insulation material and is connected to the square fixture slide rod pusher 16. Figure 7 As shown in (d), to further minimize heat loss and reduce the equivalent heat transfer coefficient to meet the boundary conditions for quasi-synchronous temperature rise, the fixture applies downward pressure from the upper aluminum plate, while the surrounding sliding rods apply pressure from the outside inward, ensuring close contact between the aerogel insulation material and the centrally located square lithium battery, eliminating any contact gaps.

[0108] This fixture accommodates battery measurements of any size and quantity, enabling measurement of multiple batteries by accumulating them within the fixture. This eliminates the need for custom molds based on battery size, reducing testing costs and significantly improving efficiency. By continuously heating and acquiring quasi-synchronous temperature rise curves at different temperature stages and varying the battery's state of charge, thermal parameters can be determined at various temperatures and SOC levels.

[0109] like Figure 8As shown, this is a verification of the quasi-synchronous temperature rise of the embodiment of the present application. By measuring the standard sample pure titanium of the same size as Application Example 1 and Application Example 2 respectively, and performing the same processing steps on them, so that their heating temperature rise is within 10°C, it can be found that the two temperature rise rates tend to be consistent after heating for 500s, ensuring that they have entered the quasi-synchronous temperature rise state.

[0110] According to the above application case 1, thermal parameters of different types of cylindrical lithium batteries are measured, such as Figure 9 and Figure 10 As shown, there are significant differences in the axial thermal conductivity and specific heat capacity of different types of cylindrical lithium batteries. Therefore, it can be concluded that the measurement method and device of the present application are applicable to the measurement of thermal parameters of various types of cylindrical lithium batteries.

[0111] like Figure 11 As shown in the figure, the second application case measures the thermal parameters of square lithium batteries of different brands, showing that there are significant differences in the thermal conductivity of square lithium batteries of different brands. This shows that the measurement method and device of this application are applicable to the measurement of various types of square lithium batteries.

[0112] At the same time, the thermal conductivity of the same square lithium battery in different directions was measured, and the changes in thermal conductivity at different temperatures and different SOCs were measured. Figure 12 As shown. The measured thermal conductivity in the length direction is 22.165-24.297 , the thermal conductivity in the thickness direction is 2.275-2.370 The thermal conductivity in the height direction is 16.998-17.813 . It shows that the battery exhibits significant thermal anisotropy characteristics.

[0113] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for measuring thermal parameters of a lithium battery, characterized in that: The method comprises the following steps: S1: Build a composite thermal conductive test structure on the end face of the lithium battery and use a fixture to encapsulate it; S2: Place the packaged battery fixture in a precision constant temperature and humidity chamber, connect the heating and temperature measuring equipment, stabilize the initial ambient temperature, and eliminate ambient temperature disturbances; S3: Apply constant power for directional heating, and continue heating until the lithium battery temperature reaches the required upper temperature limit, and simultaneously collect dynamic temperature rise data on all directions; S4: Calibrate the additional heat capacity by measuring a high-purity titanium standard sample to determine the additional heat capacity value of the fixture; S5: Obtain the energy conservation equation for one-dimensional heat conduction considering heat loss, and measure the specific heat capacity and anisotropic thermal conductivity of lithium batteries under temperature changes through quasi-synchronous temperature rise curves and model multi-parameter identification.

2. The method for measuring thermal parameters of a lithium battery according to claim 1, wherein: For square, soft-pack, and blade lithium batteries, the composite thermal conductive test structure is constructed as follows: a thermal conductive silicon pad, a copper sheet, and a thermal conductive silicon pad are arranged below the lithium battery; the same arrangement is followed above the lithium battery, and a heating film is added to contact the copper sheet for uniform heating. For cylindrical lithium batteries, the composite thermal conductive test structure is constructed as follows: a thermal conductive silicon pad and a copper sheet are arranged on the positive end surface of the lithium battery; a thermal conductive silicon pad and a copper sheet are symmetrically arranged on the negative end surface of the lithium battery, and then a heating film is contacted with the copper sheet for uniform heating.

3. The method for measuring thermal parameters of a lithium battery according to claim 2, wherein: The copper sheet is an embedded thermocouple copper sheet; For square, soft-pack and blade lithium batteries, the embedded positions of the thermocouples include: the center point of the top, the center point of the upper long side, the center point of the upper wide side and the center point of the bottom; For cylindrical lithium batteries, the embedded positions of the thermocouples include: the center point of the positive terminal surface, the center point of the negative terminal surface, any point on the boundary of the positive terminal surface, and any point on the boundary of the negative terminal surface; wherein, any point on the boundary of the positive terminal surface and any point on the boundary of the negative terminal surface are symmetrical in the vertical direction.

4. A method for measuring thermal parameters of a lithium battery according to claim 2 or 3, characterized in that: The outer layer of the cylindrical lithium battery fixture is composed of a Teflon fixture, and the inner layer is filled with aerogel insulation material. The side is locked by a locking device to ensure that the wrapping material is in close contact with the side of the lithium battery; the end face is pushed by a cylindrical fixture sliding rod to ensure that the aerogel insulation material is in close contact with both ends of the lithium battery.

5. A method for measuring thermal parameters of a lithium battery according to claim 2 or 3, characterized in that: The outer layer of the fixture for the square, soft-pack and blade lithium batteries is a metal aluminum plate, and the upper and lower surfaces of the inner layer in contact with the battery are provided with aerogel insulation material; aerogel insulation material is provided around the ring battery and connected to the slide rod push device; The clamp applies downward pressure by an upper metal aluminum plate, and sliding rods around it apply pressure from the outside to the inside, so that the aerogel insulation material is in close contact with the battery.

6. The method for measuring thermal parameters of a lithium battery according to claim 1, wherein: The S5 is specifically: S51: Obtain the energy conservation equation for one-dimensional heat conduction considering heat loss, as well as the temperature rise rate at both end surfaces of the battery and the ambient temperature set in the constant temperature and humidity chamber; S52: performing a quasi-synchronous temperature rise parameter identification method on the energy conservation equation to obtain an equivalent heat transfer coefficient of the entire fixture and a specific heat capacity of the lithium battery; S53: Substitute the obtained equivalent heat transfer coefficient into the thermal conductivity calculation formula that takes heat loss into account to obtain the anisotropic thermal conductivity of the lithium battery.

7. A method for measuring thermal parameters of a lithium battery according to claim 6, characterized in that: The S52 is specifically as follows: According to the characteristics of quasi-synchronous temperature rise, the temperature rise rate of any cross section in the lithium battery is consistent, and the energy conservation equation is time-integrated and globally equivalently processed; By fitting, we get an equation for a three-dimensional function: ,in and are the coefficients of the three-dimensional functional equation, is a constant; Equivalent specific heat capacity of lithium batteries ,in is the mass of the lithium battery; equivalent heat transfer coefficient ,in Indicates the overall surface area of ​​the lithium battery; The additional heat capacity is calibrated to obtain the specific heat capacity of the lithium battery.

8. A method for measuring thermal parameters of a lithium battery according to claim 6 or 7, characterized in that: For square, soft pack and blade lithium batteries, the anisotropic thermal conductivity includes 、 and ,in They are the length, height and thickness of the lithium battery respectively; For cylindrical lithium batteries, the anisotropic thermal conductivity includes axial thermal conductivity and radial thermal conductivity.

9. A method for measuring thermal parameters of a lithium battery according to claim 8, characterized in that: The S53 is specifically: For square, soft-pack and blade lithium batteries: multiply the equivalent heat transfer coefficient, the corresponding cross-sectional area and the temperature difference at both ends to obtain the heat flow of heat loss; substitute the difference between the heat flow in the longitudinal direction and the heat flow of heat loss into the thermal conductivity calculation formula that takes into account the heat loss, and obtain ; Calculate the vector angle between the heat flow in the length direction and the heat absorbed by the battery, and substitute it into the thermal conductivity calculation formula considering heat loss to obtain and ; For cylindrical lithium batteries: subtract the heat loss heat flux from the incoming heat flux density to obtain the axial heat flux flowing through the cylindrical lithium battery; substitute the heat loss into the thermal conductivity calculation formula to obtain the axial thermal conductivity; subtract the heat absorbed by the battery itself from the axial heat flow, and then calculate the vector angle to obtain the radial heat flow; substitute the result into the thermal conductivity calculation formula to obtain the radial thermal conductivity.

10. A device for implementing a method for measuring thermal parameters of a lithium battery according to any one of claims 1 to 9, characterized in that: include: Constant power excitation module: uses a regulated DC power supply system to achieve constant power output to the heating film through PID closed-loop control, ensuring a uniform heat flux field on the surface of the lithium battery and achieving controllable quasi-steady-state temperature rise conditions; Data acquisition module: integrated thermocouple temperature measurement system, equipped with multi-channel data acquisition card and anti-interference shielding technology, used to achieve real-time monitoring and data recording of lithium battery temperature; Sample packaging module: Develop corresponding packaging fixtures based on the shape of lithium batteries to reduce heat loss in experiments; Environmental control module: uses a programmable precision constant temperature and humidity chamber to provide ±0.1°C temperature control accuracy and ±2%RH humidity stability, establishing ideal thermodynamic boundary conditions for lithium batteries and isolating environmental disturbances.

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