Test device and test method of thermal conductivity of lithium ion battery

Abstract

To provide inventions related to the field of battery testing, in particular, to a test device and a test method of thermal conductivity of lithium ion batteries.SOLUTION: A test method includes: acquiring test temperatures collected by a first thermocouple and a second thermocouple within a set time interval following attainment of a quasi-steady state after being heated to the quasi-steady state of batteries; constructing a simulation model; inputting battery thermal conductivity rates of a plurality of sets to the simulation model to acquire a plurality of sets of simulation temperatures to be output by the simulation model; and determining a battery thermal conductivity rate on the basis of the test temperature collected by the second thermocouple and the plurality of sets of simulation temperatures. The present inventions can realize correct, rapid, and safe measurement of thermal conductivity rates.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to the field of battery testing, and more particularly to a testing device and method for the thermal conductivity of lithium-ion batteries. [Background technology]

[0002] Thermal conductivity is an important parameter for lithium-ion batteries, so accurate measurement of thermal conductivity is crucial. Currently, there are several methods for measuring the thermal conductivity of lithium-ion batteries. One method involves using the thermal conductivity of materials connected in series and parallel to the battery to obtain the overall thermal conductivity of the battery. This method does not take into account the uncertainty of the thermal contact resistance of materials inside the battery, resulting in inaccurate thermal conductivity. The other method involves testing thermal conductivity using the standard program method (steady-state method) or the modified standard program method. These methods are based on Fourier's law and require the assumption of one-dimensional heat conduction in the model. Therefore, they can only measure thermal conductivity in a single direction. Furthermore, due to the external shape of lithium-ion batteries, steady-state measurements cannot be performed for a specific direction of a battery. Furthermore, the battery requires a long heating time to reach a steady state, which can lead to thermal runaway and safety issues. Therefore, a method for quickly measuring equivalent anisotropic thermal conductivity with high accuracy is urgently needed. It is with this in mind that the present invention is particularly proposed. Summary of the Invention [Problem to be solved by the invention]

[0003] An object of the present invention is to provide a testing device and a testing method for the thermal conductivity of a lithium ion battery that can solve the problem of not being able to measure the anisotropic thermal conductivity of a lithium ion battery accurately, quickly, and safely. [Means for solving the problem]

[0004] In order to achieve the above object, the present invention uses the following technical means. In a first aspect, the present invention provides a testing device for the thermal conductivity of a lithium-ion battery, the testing device comprising a first battery and a second battery arranged in parallel, a heating film arranged between the first battery and the second battery, and an area of ​​the heating film being smaller than a contact area between the first battery and the second battery; a first thermocouple is disposed at a central position of the heating film, and the first thermocouple is used to collect the temperature at the central position after the heating film is energized; At least two second thermocouples are provided on the upper surface of the first battery and the lower surface of the second battery, respectively, and the second thermocouples are used to collect temperatures at each position of the first battery and the second battery after the heating film is energized.

[0005] In a second aspect, the present invention provides a method for testing the thermal conductivity of a lithium ion battery, the method comprising: performing a test using the above-described lithium ion battery thermal conductivity testing device; The test method is: obtaining test temperatures collected by the first thermocouple and the second thermocouple within a set time period after the battery is heated to a quasi-steady state; Building a simulation model; Inputting a plurality of sets of battery thermal conductivities into the simulation model and obtaining a plurality of sets of simulation temperatures output by the simulation model; and determining a battery thermal conductivity based on the test temperature collected by the second thermocouple and a plurality of sets of the simulation temperatures.

[0006] Compared with the prior art, the present invention has the following beneficial effects: The thermal conductivity testing device for lithium-ion batteries provided by the present invention comprises a first battery and a second battery arranged in parallel, with a heating film between them. The heating film is used to heat the batteries. During the heating process, the first and second thermocouples are used to collect temperatures at the center of the heating film and at specific locations on the battery surface. The collected temperatures can then be used to calculate the battery's thermal conductivity. Unlike the conventional infinite plate model based on Fourier's law, this device can test the thermal conductivity of the battery in all directions. It is not affected by battery shape (e.g., the thinness of soft-pack batteries makes it impossible to place a heating sheet, etc.), and can test the thermal conductivity of soft-pack, prismatic, and cylindrical batteries.

[0007] The method for testing the thermal conductivity of a lithium-ion battery provided by the present invention can determine the thermal conductivity of the battery by constructing a simulation model in combination with the test temperature collected by the above-mentioned testing device, thereby realizing accurate, rapid, and safe measurement of the thermal conductivity.

[0008] Furthermore, during testing, the device is placed in an adiabatic calorimeter to create an adiabatic environment, resulting in more accurate test results, allowing the battery to more easily enter a quasi-steady state, shortening the required heating time, increasing efficiency, and further avoiding thermal runaway, thereby improving test safety.

[0009] Furthermore, when constructing the simulation model, the simulated heating energy density is fully taken into consideration, and multiple first simulation temperatures are obtained by changing the preset heating energy density. When the first simulation temperature has the highest consistency with the test temperature collected by the first thermocouple, the corresponding preset heating energy density is the simulated heating energy density, which is more accurate than directly using the heating energy density during the actual test as the input condition of the simulation model. [Brief explanation of the drawings]

[0010] In order to more clearly describe the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly describe the drawings that need to be used to describe the specific embodiments or the prior art. It is obvious that the drawings in the following description are some embodiments of the present invention, and those skilled in the art can further obtain other drawings based on these drawings without any creative efforts. [Figure 1] FIG. 1 is a schematic diagram illustrating the configuration of a testing device for the thermal conductivity of a lithium ion battery according to Example 1. [Figure 2] FIG. 10 is a schematic diagram of a flow chart of a test method for the thermal conductivity of a lithium ion battery in Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0011]

[0023] The following description of exemplary embodiments of the present application will be given with reference to the accompanying drawings. For ease of understanding, various details of the embodiments of the present application are included, which should be considered as merely illustrative. Therefore, those skilled in the art should recognize that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of the present application. Similarly, for clarity and conciseness, the following description will omit descriptions of known functions and structures.

[0012] As described in the background art, the prior art has problems such as inaccurate thermal conductivity testing, low testing efficiency, inability to test anisotropic thermal conductivity, and low safety. Therefore, the present invention uses a specific testing device and testing method to realize accurate, rapid, safe, and reliable testing of the anisotropic thermal conductivity of a battery. The present invention will be described in more detail below with reference to examples.

[0013] Example 1 As shown in FIG. 1, this embodiment provides a testing device for the thermal conductivity of a lithium-ion battery, The test device includes a first battery 1 and a second battery 2 arranged in parallel, and a heating film 3 is provided between the first battery 1 and the second battery 2, and the area of ​​the heating film 3 is smaller than the contact area between the first battery 1 and the second battery 2; a first thermocouple is provided at a center position M0 of the heating film, and the first thermocouple is used to collect the temperature of the center position M0 after the heating film 3 is energized; At least two second thermocouples are provided on the upper surface of the first battery 1 and the lower surface of the second battery 2, respectively, and the second thermocouples are used to collect temperatures at each position of the first battery 1 and the second battery 2 after the heating film 3 is energized.

[0014] Optionally, the heating film is a polyimide heating film. Preferably, the area of ​​the heating film is much smaller than the contact area between the first battery and the second battery, i.e., the smaller the area of ​​the heating film, the better. Optionally, the heating film is square or circular.

[0015] Optionally, the first thermocouple is an ultra-fine T-type thermocouple (class I accuracy, wire diameter 0.08 mm, i.e., the diameter of a single thermocouple wire in the thermocouple is 0.08 mm). The ultra-fine T-type thermocouple is used to minimize the gap between the batteries and to minimize the influence of contact thermal resistance on the temperature.

[0016] Optionally, the second thermocouple is a common T-type thermocouple (class I accuracy, wire diameter 0.255 mm, i.e., the diameter of a single thermocouple wire within the thermocouple is 0.255 mm), and may also be an R-type, B-type, S-type, etc. thermocouple.

[0017] Generally, K-type thermocouples are commonly used to detect the temperature of new energy batteries. As can be seen from the standard EN 60584-2, its Class I accuracy means that the measurement error at low temperatures (e.g., -40°C to 375°C) is ±1.5°C. In this embodiment, T-type thermocouples are used as the first and second thermocouples, and they both have Class I accuracy, that is, the measurement error at low temperatures (e.g., -40°C to 375°C) is ±0.5°C, which makes the test results more accurate.

[0018] The above "battery" may be a soft-pack battery, a prismatic battery, or a cylindrical battery, and in this embodiment, a soft-pack battery will be described as an example.

[0019] As can be seen, the number of second thermocouples provided on the upper surface of the first battery is at least two, and the number of second thermocouples provided on the lower surface of the second battery is at least two, and in this way, measurement of thermal conductivity can be achieved.

[0020] In an alternative embodiment, the second thermocouple on the upper surface of the first battery is provided at a first point position and another point position spaced a certain distance from the first point position, the second thermocouple on the underside of the second battery is provided at a second point position and another point position spaced a certain distance from the second point position; The first point position is the position closest to the center position of the heating film on the upper surface of the first battery, and the second point position is the position closest to the center position of the heating film on the lower surface of the second battery, and the second thermocouple on the upper surface of the first battery and the second thermocouple on the lower surface of the second battery are arranged symmetrically with the plane on which the heating film is located as the plane of symmetry.

[0021] In an alternative embodiment, as shown in FIG. 1 , the second thermocouples on the top surface of the first battery 1 are provided at a first point M1, a third point M3, a fifth point M5, and a seventh point M7 arranged along the length direction of the first battery 1, and a ninth point M9 and an eleventh point M11 arranged along the width direction of the first battery 1; The second thermocouples on the underside of the second battery 2 are provided at a second point position M2, a fourth point position M4, a sixth point position M6 and an eighth point position M8 arranged along the length direction of the second battery 2, and a tenth point position M10 and a twelfth point position M12 arranged along the width direction of the second battery 2.

[0022] Although the present invention does not strictly limit the specific installation position of the second thermocouple, in order to simplify and improve the accuracy of the test results, in this embodiment, preferably, the distance between each two adjacent point positions is equal, and the connection lines between each point position and the adjacent point position are arranged parallel to the length and width directions of the battery.

[0023] In an alternative embodiment, the first point position, the third point position, the fifth point position, and the seventh point position are arranged in this order at intervals of 10 to 30 mm. The first point position, the ninth point position, and the eleventh point position are arranged in this order at intervals of 10 to 30 mm. The second point position, the fourth point position, the sixth point position, and the eighth point position are arranged in this order at intervals of 10 to 30 mm. The intervals between the second point position, the tenth point position, and the twelfth point position are each 10 to 30 mm.

[0024] As can be understood, "arranged in order at intervals of 10 to 30 mm" as described above means that each adjacent point is 10 to 30 mm apart. For example, the first and third points are 10 to 30 mm apart, the third and fifth points are 10 to 30 mm apart, and the fifth and seventh points are 10 to 30 mm apart. The intervals are independently 10 mm, 12 mm, 14 mm, 16 mm, 18 mm, 20 mm, 22 mm, 24 mm, 26 mm, 28 mm, or 30 mm. The intervals were determined by screening based on the heating time and a contour plot of the simulation. In this example, the intervals were all 10 mm.

[0025] In this embodiment, the lithium-ion battery thermal conductivity test device can measure the temperature of each thermocouple in real time after the heating film is energized, and the measured temperature can be used to calculate the battery thermal conductivity. Unlike the conventional infinite plate model based on Fourier's law, this device can test the thermal conductivity of the battery in each direction, and is not affected by the battery shape (e.g., the thickness of a soft-pack battery is too small to accommodate a heating sheet), so it can test the thermal conductivity of soft-pack, prismatic, and cylindrical batteries.

[0026] Example 2 As shown in FIG. 2 , this embodiment provides a method for testing the thermal conductivity of a lithium ion battery, which is performed using the testing device for the thermal conductivity of a lithium ion battery described in embodiment 1, and includes the following steps: In S110, the test device for the thermal conductivity of the lithium ion battery is placed in an adiabatic calorimeter.

[0027] By placing the device in an adiabatic calorimeter (ARC), the device is in an adiabatic environment, making the test results more accurate. Conventional devices are generally placed in insulating materials, which cannot achieve complete insulation, resulting in too large deviations in the test results.

[0028] In S120, the battery is heated, and test temperatures collected by the first and second thermocouples are acquired within a set time period from when the battery reaches a quasi-steady state.

[0029] In an alternative embodiment, the quasi-steady state is determined as follows: after energizing the heating film, if the temperatures at the first and second points are both a first fixed value or within a set deviation of the first fixed value, or if the temperature difference between the first point and the center of the heating film and the temperature difference between the second point and the center of the heating film are both a second fixed value and maintained for a set time, or if the two temperature differences are both a second fixed value or within a set deviation of the second fixed value, the quasi-steady state is determined to have been entered.

[0030] After the heating film is energized, the temperatures at the first and second points gradually increase over time and reach a stable value (which may fluctuate around this value). This indicates that the battery has entered a quasi-steady state. This stable value is the "first fixed value." As can be seen, this first fixed value is not a preset value. Naturally, this determination can also be made by comparing the temperature difference between the first point and the center of the heating film with the temperature difference between the second point and the center of the heating film. The quasi-steady state is determined to have been entered when both temperature differences are the second fixed value and maintained for a preset time, or when both temperature differences are the second fixed value or within a preset deviation of the second fixed value. Like the first fixed value, this second fixed value is not a preset value.

[0031] The "set time" mentioned above is a preset value, generally an empirical value, and may be 500 to 1000 ms, but in this embodiment, 1000 ms is selected. That is, what is acquired in step S120 is the test temperature for the period from when the quasi-steady state is reached until 1000 ms has elapsed. As can be seen, the acquired test temperature changes over time, and thus, multiple curves showing the temperature change over time can be obtained, which can be called test curves.

[0032] It should be noted that throughout the test, if the test temperature collected by the second thermocouple exceeds the battery's safety temperature (provided by the battery manufacturer; if not, it can be set to 55°C), the test must be forcibly terminated to prevent any danger from occurring.

[0033] In S130, a simulation model is constructed.

[0034] In an alternative embodiment, constructing the simulation model comprises: Building an initial simulation model based on the temperature-dependent specific heat capacity of the battery, the battery density, the heating film density, the specific heat capacity of the heating film, and the thermal conductivity of the heating film; Input a plurality of preset heating energy densities into the initial simulation model, and obtain a plurality of first simulation temperatures output from the initial simulation model, wherein the first simulation temperatures are simulation temperatures at the center position of the heating film; A simulation model is determined based on the test temperature collected by the first thermocouple and the plurality of first simulation temperatures, the simulation model including a simulated heating energy density, the simulated heating energy density being a preset heating energy density that most closely matches the first simulation temperature and the test temperature collected by the first thermocouple.

[0035] Here, the temperature-dependent specific heat capacity of the battery is the specific heat capacity during a set time interval after the battery enters a quasi-steady state. The temperature-dependent specific heat capacity of the battery, the battery density, the heating film density, the heating film specific heat capacity, and the heating film thermal conductivity are all known values. The temperature-dependent specific heat capacity of the battery can be calculated using the following formula: JPEG2025178179000002.jpg16170 where Cp is the temperature change specific heat capacity, P is the heat generation power (i.e., the power to heat the heating film), m is the weight of the battery, and dT / dt is the time rate of change of temperature during the period from when the battery reaches a quasi-steady state until a set time has elapsed.

[0036] The simulation model can be constructed using Ansys Fluent software. When the temperature-dependent specific heat capacity of the battery, the battery density, the heating film density, the specific heat capacity of the heating film, and the thermal conductivity of the heating film are input, the model automatically launches and calculates the energy equation and outputs the simulation temperature.

[0037] In this embodiment, the simulated heating energy density is fully taken into consideration when constructing the simulation model, and multiple first simulation temperatures are obtained by changing the preset heating energy density. When the first simulation temperature has the highest consistency with the test temperature collected by the first thermocouple, the corresponding preset heating energy density is the simulated heating energy density, which is more accurate than directly using the heating energy density during the actual test as the input condition for the simulation model.

[0038] In S140, a plurality of sets of battery thermal conductivities are input to the simulation model, and a plurality of sets of simulation temperatures output by the simulation model are obtained.

[0039] Here, "battery thermal conductivity" includes the thermal conductivity in the three directions of the battery: x, y, and z. Therefore, multiple sets of thermal conductivities are input to the simulation model, and each set includes the thermal conductivity in the three directions. Furthermore, the output simulation temperature is the simulation temperature at each point on the battery (which is the same as the point on the test equipment), and this simulation temperature is a curve in which the temperature changes over time, which can be called a simulation curve.

[0040] In S150, a battery thermal conductivity is determined based on the test temperature collected by the second thermocouple and the plurality of sets of the simulation temperatures.

[0041] In an alternative embodiment, determining a battery thermal conductivity based on the test temperature collected by the second thermocouple and the plurality of sets of the simulation temperatures includes: performing data processing on the test temperatures collected by the second thermocouple, and determining an average value of the test temperatures at symmetrical points on the first battery and the second battery as a test characteristic temperature, and there are a plurality of test characteristic temperatures; The method includes comparing the test characteristic temperature with a plurality of sets of the simulation temperatures, and determining the thermal conductivity corresponding to the simulation temperature that most closely matches the test characteristic temperature as the battery thermal conductivity.

[0042] As can be understood, the "symmetrical points" refer to points symmetrically arranged on the first and second batteries with the plane on which the heating film is located as the symmetry plane. For example, the first point M1 and the second point M2 in FIG. 1 are a pair of symmetrical points, and the average value of the test temperatures at the first point M1 and the second point M2 is calculated as the first characteristic temperature. The third point M3 and the fourth point M4 are a pair of symmetrical points, and the average value of the test temperatures at the third point M3 and the fourth point M4 is calculated as the second characteristic temperature. There are also multiple test characteristic temperatures.

[0043] Optionally, the test characteristic temperature is compared to the simulation temperature by the following formula: JPEG2025178179000003.jpg18164However, RMSE is the simulation deviation, T s is the test characteristic temperature, T fis the simulation temperature, and n is the length of the time interval, which is the length of the set time interval after the battery is heated to a quasi-steady state and then reaches the quasi-steady state. The smaller the RMSE, the better, and the closer the simulation temperature matches the test feature temperature, the better the match. This formula is an evaluation of the match of a feature point. For all feature points of the battery, the average value of all RMSEs is taken, and the thermal conductivity corresponding to the smallest average RMSE is selected as the thermal conductivity of the battery.

[0044] The above-mentioned method for testing the thermal conductivity of a lithium-ion battery determines the battery thermal conductivity by constructing a simulation model in combination with the test temperature collected by the above-mentioned testing device, thereby realizing accurate, rapid, and safe measurement of the thermal conductivity.

[0045] It should be understood that steps can be rearranged, added, or deleted using various types of flows shown above. For example, the steps described in this application may be performed in parallel, sequentially, or in a different order, and are not limited herein as long as the desired results of the technical solutions disclosed in this application can be achieved.

[0046] The above specific embodiments do not limit the scope of protection of the present application. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present application should be included within the scope of protection of the present application.

Claims

1. A method for testing the thermal conductivity of a lithium-ion battery, comprising: The test method includes performing a test using a thermal conductivity test device for a lithium ion battery, the testing device includes a first battery and a second battery arranged in parallel, a heating film is provided between the first battery and the second battery, and the area of ​​the heating film is smaller than the contact area between the first battery and the second battery; a first thermocouple is disposed at a central position of the heating film, and the first thermocouple is used to collect the temperature at the central position after the heating film is energized; At least two second thermocouples are provided on the upper surface of the first battery and the lower surface of the second battery, respectively, and the second thermocouples are used to collect temperatures at each position of the first battery and the second battery after the heating film is energized; The test method comprises: obtaining test temperatures collected by the first thermocouple and the second thermocouple within a set time after the battery reaches a quasi-steady state through heating; Building a simulation model; Inputting a plurality of sets of battery thermal conductivities into the simulation model and obtaining a plurality of sets of simulation temperatures output by the simulation model; determining a battery thermal conductivity based on the test temperature collected by the second thermocouple and a plurality of sets of the simulation temperatures; Constructing the simulation model includes: Constructing an initial simulation model based on a temperature-dependent specific heat capacity of a battery, a battery density, a heating film density, a specific heat capacity of the heating film, and a thermal conductivity of the heating film, wherein the temperature-dependent specific heat capacity of the battery is the specific heat capacity within the set time after the battery reaches the quasi-steady state; Inputting a plurality of preset heating energy densities into the initial simulation model, and obtaining a plurality of first simulation temperatures output from the initial simulation model, wherein the first simulation temperatures are simulation temperatures at a center position of the heating film; determining the simulation model based on the test temperature collected by the first thermocouple and the first plurality of simulation temperatures, wherein the simulation model includes a simulated heating energy density, the simulated heating energy density being a preset heating energy density that most closely matches the first simulation temperature and the test temperature collected by the first thermocouple. A method for testing the thermal conductivity of a lithium-ion battery.

2. 2. The method for testing the thermal conductivity of a lithium ion battery according to claim 1, further comprising placing the device in an adiabatic calorimeter before acquiring test temperatures collected by the first and second thermocouples within a set time after the battery has reached a quasi-steady state by heating.

3. 2. The method for testing the thermal conductivity of a lithium ion battery according to claim 1, wherein after the heating film is energized, it is determined that the quasi-steady state has been reached if the temperatures at the first point position and the second point position are both a first fixed value or within a set deviation of the first fixed value, or if the temperature difference between the first point position and the center position of the heating film and the temperature difference between the second point position and the center position of the heating film are both a second fixed value and are maintained for a set time, or if the two temperature differences are both a second fixed value or within a set deviation of the second fixed value.

4. Determining a battery thermal conductivity based on the test temperature collected by the second thermocouple and a plurality of sets of the simulation temperatures includes: performing data processing on the test temperatures collected by the second thermocouple, and determining an average value of the test temperatures at symmetrical points on the first battery and the second battery as a test characteristic temperature in the data processing; and 2. The method for testing the thermal conductivity of a lithium ion battery according to claim 1, further comprising: comparing the test characteristic temperature with a plurality of sets of the simulation temperatures; and determining, as the battery thermal conductivity, the thermal conductivity corresponding to the simulation temperature that most closely matches the test characteristic temperature.

5. the second thermocouple on the upper surface of the first battery is provided at a first point position and another point position spaced a certain distance from the first point position; the second thermocouple on the underside of the second battery is provided at a second point position and another point position spaced a certain distance from the second point position; 2. The method for testing the thermal conductivity of a lithium ion battery according to claim 1, wherein the first point is a point on the upper surface of the first battery that is closest to the center position, the second point is a point on the lower surface of the second battery that is closest to the center position, and the second thermocouple on the upper surface of the first battery and the second thermocouple on the lower surface of the second battery are arranged symmetrically with respect to a plane on which the heating film is located.

6. the second thermocouples on the upper surface of the first battery are provided at a first point position, a third point position, a fifth point position, and a seventh point position arranged along the length direction of the first battery, and a ninth point position and an eleventh point position arranged along the width direction of the first battery; 6. The method for testing the thermal conductivity of a lithium ion battery according to claim 5, wherein the second thermocouples on the underside of the second battery are provided at a second point, fourth, sixth, and eighth points arranged along the length direction of the second battery, and tenth and twelfth points arranged along the width direction of the second battery.

7. The first point position, the third point position, the fifth point position, and the seventh point position are arranged in this order at intervals of 10 to 30 mm, 7. The method for testing the thermal conductivity of a lithium ion battery according to claim 6, wherein the first point position, the ninth point position, and the eleventh point position are arranged at intervals of 10 to 30 mm in sequence.

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