A method and device for measuring temperature-dependent thermal parameters of a lithium battery

Abstract

The present application 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. In consideration of heat loss, the specific heat capacity and anisotropic thermal conductivity of lithium batteries under temperature change can be synchronously measured through single experiment, greatly improving the test efficiency and measurement accuracy. The present application is suitable for cylindrical, square, soft package and blade lithium batteries, and can be measured under various different equivalent heat exchange boundary conditions, including air natural convection, heat insulation material wrapping, vacuum, heat insulation calorimeter, etc., and is convenient to operate, high in accuracy and strong in adaptability, and can realize rapid and accurate measurement of thermal parameters of lithium batteries at different temperatures, giving consideration to high efficiency and high accuracy.

Description

TECHNICAL FIELD

[0001] The application 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. BACKGROUND

[0002] In recent years, electric vehicles have played an important role in alleviating energy crisis and environmental pollution. Lithium ion batteries have high energy density, long service life, low self-discharge rate and other advantages, and have become the preferred power supply for electric vehicles.

[0003] However, the characteristics of lithium ion batteries are closely related to the working temperature. When the battery temperature reaches a high threshold, the solid electrolyte interface layer will decompose, and even worse, the battery will be out of control and accompanied by smoke, fire or explosion. On the other hand, low temperature leads to increased internal resistance, and the battery discharge capacity and electric vehicle driving performance decrease sharply. Obviously, the safety of lithium ion battery thermal management has become an important problem in the development of electric vehicles. Thermal parameters are necessary parameters for battery thermal management system modeling, simulation and control. In-depth study of lithium ion battery thermal parameters is very necessary for accurately predicting battery temperature changes, improving battery performance, prolonging service life, and even suppressing and eliminating thermal runaway disasters. It has important 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 the specific heat capacity change with temperature, so it is particularly important to measure the thermal parameters under temperature change in lithium battery testing and research. The thermal parameters under temperature change can better reflect the true state of lithium batteries in actual application.

[0005] The lithium battery thermal parameter measurement method is mainly divided into steady-state and transient-state methods. The steady-state method measures the thermal conductivity by establishing a stable temperature gradient field and using the Fourier heat conduction law. The measurement results have high accuracy and reliability, but the test process is complex, and it takes a long time to reach thermal equilibrium. The transient-state method is based on non-steady-state heat transfer theory, which measures 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 the results is slightly insufficient compared to the steady-state method. The quasi-steady-state method is between the steady-state method and the transient-state method. This method uses the thermal response characteristics during the formation of the steady-state process. When the temperature rise rate of each position in the sample is approximately the same, a more accurate measurement result 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 period, and has high practical value in engineering applications.

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

[0007] (1) Quasi-steady-state method can only be single measurement, variable temperature measurement, the experimental measurement efficiency is low, need to set different initial ambient temperature to carry out variable temperature measurement.

[0008] (2) Quasi-steady-state method for measuring the thermal conductivity of lithium battery, single experiment can only measure the thermal conductivity of one direction, not convenient for efficient measurement of lithium battery anisotropy thermal conductivity.

[0009] (3) Adiabatic quasi-steady-state measurement method, in order to ensure that the battery is in the adiabatic boundary condition for experiment, need to carry on the vacuumizing or set up the adiabatic boundary condition and handle, process is complicated, operation is complex. 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 needs to measure the temperature rise and temperature drop of the lithium battery, and the heat loss of the temperature rise process is calculated through the temperature drop process, and then the lithium battery thermal conductivity and specific heat capacity are calculated. The test time cost is greatly increased, and the test process of one temperature stage lasts for 3-4 hours. The heat loss in the temperature rise and temperature drop processes is not completely consistent, and the specific heat capacity measurement error of small samples will be larger.

[0011] (5) Adiabatic quasi-steady-state measurement method and calibration calorimetry method need to wrap the lithium battery with adiabatic material, there is no specific device for wrapping and packaging, and the wrapping degree of each experiment is different, which will affect the accuracy of the measurement. SUMMARY

[0012] In view of the above-mentioned deficiencies of the prior art, the purpose of the present application is to provide a lithium battery temperature change thermal parameter measurement method and device.

[0013] In order to achieve the above-mentioned purpose, the first aspect of the present application provides a lithium battery temperature change thermal parameter measurement method, comprising:

[0014] S1: Constructing a composite thermal conductivity test structure on the end face of the lithium battery, and using a clamp for packaging.

[0015] S2: Placing the packaged battery clamp in a precision constant temperature and humidity box, connecting heating and temperature measuring equipment, stabilizing the initial ambient temperature, and eliminating environmental temperature disturbance.

[0016] S3: Apply constant power for directional heating, continue heating until the lithium battery temperature reaches the required upper limit of temperature, and synchronously collect the dynamic temperature rise data of each direction.

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

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

[0019] The second aspect of the application provides a device for realizing the above-mentioned lithium battery temperature change heat parameter measurement method, which adopts a modular design and mainly includes the following core functional modules:

[0020] Constant power excitation module: a high-precision stabilized DC power supply system is used to realize constant power output of the heating film, ensure the formation of a uniform heat flux density field on the surface of the lithium battery, and realize controllable quasi-synchronous temperature rise conditions.

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

[0022] Sample packaging module: according to the shape of the lithium battery, the corresponding packaging fixture is developed, and the heat loss of the experiment is greatly reduced by using aerogel thermal insulation material. The fixture is easy to operate and can package batteries of different sizes.

[0023] Environment control module: use programmable precision constant temperature and humidity box to provide temperature control accuracy of ±0.1℃ and humidity stability of ±2%RH, to establish ideal thermodynamic boundary conditions for lithium batteries and effectively isolate environmental disturbances.

[0024] Overall, compared with the prior art, the present application has the following significant advantages:

[0025] 1. The present application can simultaneously measure the specific heat capacity and anisotropic thermal conductivity of the lithium battery under temperature change by a single experiment, greatly improving the test efficiency and measurement accuracy.

[0026] 2. The present application is suitable for cylindrical, square, soft package and blade lithium batteries, and can be measured under various equivalent heat exchange boundary conditions, including air natural convection, heat insulation material wrapping, vacuum, heat insulation calorimeter, etc., which is convenient to operate, high in accuracy and strong in adaptability, and can realize rapid and accurate measurement of the thermal parameters of lithium batteries at different temperatures, taking into account high efficiency and high precision.

[0027] 3. The present application can adaptively identify the heat loss parameters in the measurement process without complex treatment of the lithium battery, significantly improving the repeatability and stability of the measurement. And support multi-channel automatic measurement, according to the test requirements, can continuously measure the temperature change heat parameters of multiple samples, meet the requirements of large batch testing. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is a flow chart of a lithium battery temperature change thermal parameter measurement method according to an embodiment of the present application.

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

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

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

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

[0033] Figure 6 is a device structure schematic diagram according to an application embodiment one of the present application.

[0034] Figure 7 is a device structure schematic diagram according to an application embodiment two of the present application.

[0035] Figure 8 is a temperature rise and temperature rise rate diagram of a standard sample pure titanium measured according to an embodiment of the present application.

[0036] Figure 9 is a thermal conductivity result diagram of different models of cylindrical lithium batteries measured according to an application embodiment one of the present application.

[0037] Figure 10 is a specific heat capacity result diagram of different models of cylindrical lithium batteries measured according to an application embodiment one of the present application.

[0038] Figure 11 is a thermal conductivity change trend diagram of different brands of square lithium batteries measured according to an application embodiment two of the present application.

[0039] Figure 12 is a square lithium battery thermal conductivity change trend diagram measured according to an application embodiment two of the present application.

[0040] The reference signs: 1. thermocouple, 2. round copper sheet, 3. round heat-conducting silicon pad, 4. cylindrical lithium battery, 5. round polyimide heating film, 6. lock device, 7. Teflon clamp, 8. cylindrical clamp aerogel thermal insulation material, 9. cylindrical clamp sliding rod pushing device, 10. square polyimide heating film, 11. square heat-conducting silicon pad, 12. square lithium battery, 13. square copper sheet, 14. aluminum plate, 15. square clamp aerogel thermal insulation material, 16. square clamp sliding rod pushing device. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and examples. It should be understood that the described examples are only used to end the present application and not used to limit the present application.

[0042] The present application provides a lithium battery thermal parameter measurement method and device with short test time, accurate measurement results, wide adaptation range, low test cost and easy implementation. Through a single experiment, the anisotropic thermal conductivity and the specific heat capacity of the lithium battery at different temperatures can be measured synchronously. The present application provides important data and method basis for the optimization design of the battery thermal management system. It is suggested that the anisotropic thermal conductivity of the battery should be measured in actual engineering application, and the battery thermal management strategy should be optimized according to the actual parameters.

[0043] As shown in Figure 1 The present application provides a lithium battery thermal parameter measurement method, which comprises the following steps:

[0044] S1: A composite thermal conduction test structure is constructed on the end face of the lithium battery, and the packaged battery clamp with a specially designed aerogel wrapping material is used for packaging.

[0045] For square, soft package and blade lithium batteries, the composite thermal conduction test structure is constructed in the following manner: the lithium battery is arranged in the order of "thermal conduction silicon pad-copper sheet-thermal conduction silicon pad" on the lower surface; the lithium battery is arranged in the same order on the upper surface, and a heating film is added to contact the copper sheet for uniform heating. For cylindrical lithium batteries, the composite thermal conduction test structure is constructed in the following manner: the thermal conduction silicon pad and the copper sheet are arranged on the positive electrode end face of the lithium battery; the thermal conduction silicon pad and the copper sheet are symmetrically arranged on the negative electrode end face of the lithium battery, and a heating film is added to contact the copper sheet for uniform heating.

[0046] As shown in Figure 2 In order to prevent the interference of the heating film on the temperature measurement, a thermocouple 1 is embedded in the copper sheet to collect the temperature data in the temperature rising process in real time. For square, soft package and blade lithium batteries, the embedded positions of the thermocouple 1 include: the center point of the upper surface, the center point of the long side of the upper surface, the center point of the wide side of the upper surface and the center point of the lower surface. For cylindrical lithium batteries, the embedded positions of the thermocouple 1 include: the center point of the positive electrode end face, the center point of the negative electrode end face, an arbitrary point on the boundary of the positive electrode end face and an arbitrary point on the boundary of the negative electrode end face; wherein the arbitrary point on the boundary of the positive electrode end face and the arbitrary point on the boundary of the negative electrode end face are symmetrical in the vertical direction.

[0047] It should be noted that during the contact of the lithium battery with the thermal conduction silicon pad, the copper sheet and the heating sheet, cracks should be avoided to prevent the introduction of additional thermal resistance and affect the test results.

[0048] S2: The packaged battery clamp is placed in a precision constant temperature and humidity box, the heating and temperature measurement equipment is connected, the initial environmental temperature is stabilized, and the environmental temperature disturbance is eliminated.

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

[0050] It should be noted that the constant heating power is maintained to continuously heat the lithium ion battery. After 500 seconds of testing, the system enters a quasi-synchronous temperature rise state, at which time the temperature rise rates of the battery at various cross-sectional positions tend to be consistent. Then, the test is stopped until the lithium battery temperature rises to the target temperature, and the thermal parameters at different temperatures are calculated based on the test data in different time intervals.

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

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

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

[0054] Further, the S5 specifically comprises:

[0055] S51: Obtain the energy conservation equation of one-dimensional heat conduction considering heat loss, as well as the temperature rise rate of the two ends of the battery and the environmental temperature set in the constant temperature and humidity chamber.

[0056] The energy conservation equation is:

[0057]

[0058] wherein is a constant heat flux, i.e., a constant power per unit area provided by a constant voltage and current source. S represents the cross-sectional area of the heating surface of the lithium battery, and are the mass and equivalent specific heat capacity of the lithium battery, respectively, represents an arbitrary spatial position within the lithium battery, represents the environmental temperature, is the overall equivalent heat transfer coefficient of the surface of the lithium battery. This formula establishes the dynamic relationship of the battery heat balance, indicating that the input lithium battery is mainly used for two parts: the heat capacity effect of the battery itself and the heat convection loss on the surface of the lithium battery.

[0059] S52: The quasi-synchronous temperature rise parameter identification method is performed on the energy conservation equation, and the equivalent heat exchange coefficient of the entire fixture and the specific heat capacity of the lithium battery are fitted.

[0060] It should be noted that there is heat loss in the heat transfer process, and the entire fixture is not an ideal adiabatic boundary. Temperature measurement needs to be performed on multiple spatial positions of the lithium battery to determine whether the temperature rise rates of each section are consistent to ensure that the quasi-synchronous temperature rise state is entered. Through data testing, it is found that the temperature rise rate deviation between sections is less than 0.3%, which proves that the quasi-synchronous temperature rise state is entered.

[0061] According to the characteristics of the quasi-synchronous temperature rise, the temperature rise rates of any sections in the lithium battery are consistent: , and represent any two section positions in the battery. Time integration and global equivalent processing are performed on the energy conservation equation:

[0062]

[0063] wherein and represent the starting time and the measurement end point of the lithium battery entering the quasi-synchronous temperature rise, represents a constant term, represents the total surface area of the lithium battery.

[0064] It should be noted that a three-dimensional function equation can be obtained through fitting: , and are the coefficients of the three-dimensional function equation, is a constant. The equivalent specific heat capacity of the lithium battery , and the equivalent heat exchange coefficient .

[0065] Due to the existence of additional heat capacity, calibration is required. The additional heat capacity is calibrated through a standard sample of high-purity titanium. After calibration, the specific heat capacity c li of the lithium battery is obtained.

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

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

[0068]

[0069] S53: The obtained equivalent heat exchange coefficient is substituted into the heat conduction coefficient calculation formula considering heat loss to obtain the heat conduction coefficient of the lithium battery:

[0070]

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

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

[0073]

[0074]

[0075] wherein is the temperature of the heating end of the lithium battery, is the temperature of the cold end of the lithium battery, and the equivalent heat transfer coefficient obtained is substituted, and the anisotropic thermal conductivity of the lithium battery can be calculated.

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

[0077] Further, the heat flow density flowing in is subtracted by the heat loss heat flow, and the axial heat flow flowing through the cylindrical lithium battery is obtained, and the axial thermal conductivity of the cylindrical lithium battery is obtained by substituting the heat transfer coefficient calculation formula considering heat loss:

[0078]

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

[0080] As shown in Figure 3 , there is an angle between the axial heat flow and the heat loss heat flow of the side surface , the axial heat flow flowing in is subtracted by the heat absorbed by the battery itself, and the heat flow flowing in the radial direction is obtained by vector angle calculation. The above results are substituted into the heat transfer coefficient calculation formula considering heat loss, and the radial thermal conductivity calculation formula is obtained:

[0081]

[0082] wherein is the radial thermal conductivity of the cylindrical lithium battery, is the radius of the cylindrical lithium battery, 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 the cylindrical lithium battery, .

[0083] Further, the anisotropic thermal conductivities of square, pouch and blade lithium batteries are divided into length, height and thickness directions. By giving a constant heat flux density in the length direction , the lithium battery is subjected to temperature rise. The fitted equivalent heat transfer coefficient is multiplied by the corresponding cross-sectional area and the temperature difference between the two ends to obtain the heat flow of heat loss. The difference between the inflow heat flux in the length direction and the heat flow of heat loss is substituted into the heat conduction coefficient calculation formula considering heat loss to obtain the heat conduction coefficient calculation formula in the length direction:

[0084]

[0085] Similarly, the heat flow in the length direction and the heat flow in the height and thickness directions respectively exist angles and . The difference between the inflow heat flux in the length direction and the heat absorbed by the battery is calculated by vector angle, and substituted into the heat conduction coefficient calculation formula considering heat loss to obtain the heat conduction coefficient calculation formula in the height and thickness directions:

[0086]

[0087]

[0088] wherein length, height and thickness of square, pouch and blade lithium batteries, is the path of heat conduction, is the heat flux density in the direction, and S is the cross-sectional area. , .

[0089] The lithium battery temperature change heat parameter measurement method can simultaneously measure the anisotropic thermal conductivity and the specific heat capacity of the lithium battery during temperature change through one experiment, and is suitable for measuring various types of lithium batteries without complex treatment of the lithium battery. The heat loss parameter in the measurement process can be adaptively identified, and the repeatability and stability of the measurement are significantly improved.

[0090] As shown in Figure 3 , the 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 One: Thermal Parameter Measurement of Cylindrical Lithium Batteries

[0099] This application example uses Panasonic 21700 cylindrical lithium batteries, with a capacity of 5 Ah and a mass of 65.8 g. Referring to FIG. 4A, a layer of circular heat-conducting silicone pad 3 and a layer of circular copper sheet 2 are arranged on the negative end surface of the cylindrical lithium battery 4, and a circular polyimide heating film 5 is contacted on the copper sheet for uniform heating; a layer of circular heat-conducting silicone pad 3 and a layer of circular copper sheet 2 are symmetrically arranged on the positive end surface, and the arrangement result is shown in FIG. 4B. Figure 6 Figure 6

[0100] To ensure the uniformity of the boundary conditions of the experiment, a special fixture is used to package the cylindrical lithium battery, as shown in FIG. 4D. The packaged battery fixture is placed in a high-precision constant temperature oven, and the battery temperature change is monitored. When the thermal equilibrium state is reached, a constant power input is provided to the heating module by a direct current power supply to stimulate the temperature rise behavior of the lithium battery. Figure 6

[0101] During this process, a temperature difference occurs between the positive and negative end surfaces of the battery, which is specifically represented as wherein and are the temperatures of the positive and negative end surfaces, respectively. The existence of this temperature gradient causes heat conduction within the battery, with the heat flow direction pointing from the high-temperature region to the low-temperature region. The thermal parameters of the cylindrical lithium battery can be calculated by the quasi-synchronous temperature rise parameter identification measurement method.

[0102] It should be noted that, in order to better reduce the test error, this application example one provides a capsule-shaped fixture. As shown in FIG. 4C, the outer layer of the fixture is composed of a Teflon fixture 7, the inner layer is filled with cylindrical fixture aerogel thermal insulation material 8, the side surface is tightly contacted with the lithium battery through the lock buckle device 6, and the end surface is tightly contacted with the lithium battery through the cylindrical fixture sliding rod pushing device 9, which maximizes the reduction of heat loss and reduces the equivalent heat transfer coefficient to meet the boundary conditions of quasi-synchronous temperature rise. Figure 6 This fixture is suitable for measuring cylindrical lithium batteries of any size, and the measurement of any number of cylindrical lithium batteries can be achieved by stacking the fixtures, without the need to customize molds according to the size of the cylindrical lithium battery, thereby reducing the test cost of the experiment and greatly improving the efficiency of the experiment. By continuously heating to obtain quasi-synchronous temperature rise curves at different temperature stages and changing the state of charge of the battery, thermal parameters at different temperatures and SOC states can be obtained.

[0103] Application Example Two: Thermal Parameter Measurement of Rectangular, Soft Packaged and Blade Lithium Batteries

[0104]

[0105] ​​​​The application example adopts a square hard-shell lithium battery, the size of which is , the capacity of which is 32 Ah, and the mass of which is 764.7 g. As shown in (a) of Figure 7 , a layer of square heat-conducting silicon pad 11 and a layer of square copper sheet 13 are arranged on the upper surface of the square lithium battery 12, and a square polyimide heating film 10 is added to contact the copper sheet to perform uniform heating; a layer of square heat-conducting silicon pad 11 and a layer of square copper sheet 13 are also symmetrically arranged on the lower surface, and the processed square lithium battery is placed in a specially-made clamp, as shown in (b) of Figure 7 . The packaged battery clamp is placed in a high-precision constant-temperature box, the temperature change of the battery is monitored, and when the thermal equilibrium state is reached, a constant power input is provided to the heating film by a direct-current power supply to excite the lithium battery to generate a temperature rise behavior.

[0106] During this process, a temperature difference is generated between the upper and lower surfaces of the square lithium battery, which is specifically represented as , wherein and are the temperatures of the heating end surface and the symmetric end surface, respectively. The existence of this temperature gradient causes heat conduction to occur inside the battery, and the heat flow direction is from the high-temperature area to the low-temperature area. The calculation of the thermal parameters of the square lithium battery can be performed by a quasi-synchronous temperature rise parameter identification measurement method.

[0107] As shown in (c) of Figure 7 , in order to ensure the uniformity of the experimental boundary conditions, the outer layer of the clamp is a metal aluminum plate 14, and the upper and lower surfaces in contact with the battery are provided with 20 mm thick square clamp aerogel thermal insulation material 15, the thermal conductivity of which is 0.02 . The four sides are also provided with 20 mm thick aerogel thermal insulation material, which is connected with the square clamp sliding rod pushing device 16, as shown in (d) of Figure 7 . In order to better reduce heat loss and reduce the equivalent heat exchange coefficient, the boundary conditions of the quasi-synchronous temperature rise are satisfied. The clamp applies pressure downward from the upper aluminum plate, and the sliding rods on the four sides apply pressure from the outside to the inside, so that the aerogel thermal insulation material is in close contact with the square lithium battery at the center position, avoiding the occurrence of gaps between the contacts.

[0108] The clamp is suitable for measuring any size and any number of batteries, and the measurement of multiple batteries can be realized by the accumulation of the batteries inside the clamp. Therefore, the mold does not need to be re-customized according to the size of the battery, which reduces the test cost of the experiment 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 state of charge of the battery, thermal parameters at different temperatures and SOC states can be obtained.

[0109] As shown in (e) of Figure 8 , the quasi-synchronous temperature rise curves of the square lithium battery at different temperatures and SOC states are obtained.As shown, the quasi-synchronous temperature rise verification of the embodiments of the present application is verified by measuring and applying standard sample pure titanium of the same size as application example one and application example two, and the same processing steps are performed to make the heating temperature rise within 10℃, and it can be found that the two temperature rise rates tend to be consistent after 500s of heating to ensure that the quasi-synchronous temperature rise state is entered.

[0110] According to the above application case one, the thermal parameters of different types of cylindrical lithium batteries are measured, such as Figure 9 and Figure 10 As shown, the axial thermal conductivity and specific heat capacity of different types of cylindrical lithium batteries are significantly different, so the measurement method and device of the present application are suitable for thermal parameter measurement of various types of cylindrical lithium batteries.

[0111] As shown in Figure 11 , application case two measures the thermal parameters of different brands of square lithium batteries, which shows that the thermal conductivities of different brands of square lithium batteries are significantly different. It can be seen that the measurement method and device of the present application are suitable for measuring various types of square lithium batteries.

[0112] At the same time, the thermal conductivities in different directions of the same type of square lithium battery are also measured, and the changes of thermal conductivity at different temperatures and different SOC are measured, as shown in Figure 12 The length direction thermal conductivity is 22.165-24.297 , the thickness direction thermal conductivity is 2.275-2.370 , and the height direction thermal conductivity is 16.998-17.813 . It shows that the battery presents a significant thermal anisotropy characteristic.

[0113] Those skilled in the art will readily understand that the above description is only a preferred embodiment of the present application and is not intended to limit the present application, and any modifications, equivalent replacements and improvements made within the spirit and principles of the present application shall be included in the protection scope of the present application.

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 to 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.

Images