Method for measuring heat conductivity coefficient of energy storage battery in thickness direction

Abstract

The invention discloses a method for measuring a heat conductivity coefficient in a thickness direction of an energy storage battery, which is applied to the technical field of batteries and comprises the following steps: uniformly heating two external main surfaces of two closely attached energy storage batteries at a preset environment temperature at constant power until the preset temperature is reached; substituting the temperature difference between the cold and hot surface temperatures and the preset environment temperature in the heating process into a linear fitting equation of the temperature difference and the temperature drop rate to obtain the temperature drop rate of the cold and hot surfaces, and carrying out integration on the battery heating time to obtain the temperature drop amplitude of the cold and hot surfaces caused by heat loss; correcting the temperatures of the cold surface and the hot surface when the thermal field of the battery reaches the quasi-steady state based on the temperature drop amplitude of the cold surface and the hot surface, and substituting the corrected temperatures into a thickness-direction heat conductivity coefficient theoretical model obtained based on the Fourier heat conduction law to obtain a thickness-direction heat conductivity coefficient of the energy storage battery at the to-be-measured working temperature; wherein the to-be-measured working temperature is an average value of the preset environment temperature and the preset temperature. According to the invention, the heat conductivity coefficient measurement speed and precision are effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and particularly to a method for measuring the thermal conductivity in the thickness direction of an energy storage battery. Background Art

[0002] The thermal conductivity in the thickness direction of an energy storage battery describes the ability of the battery to even out the temperature distribution. Therefore, clarifying the thermal conductivity in the thickness direction of an energy storage battery is of great significance for controlling its thermal field distribution.

[0003] The invention patent with the application publication number CN109613055A discloses a steady-state determination method and determination device for the radial thermal conductivity of a cylindrical battery, and the invention patent with the application publication number CN108170914A discloses an in-situ calculation method for the thermal conductivity of a cylindrical wound lithium-ion power battery. The invention patent with the application publication number CN115901849A discloses a method and device for measuring the radial thermal conductivity and specific heat of a cylindrical battery. These three invention patents can only be used for measuring the thermal conductivity of cylindrical power and energy storage batteries, and cannot be used for measuring the thermal conductivity in the thickness direction of square and soft-pack energy storage batteries.

[0004] The invention patent with the application publication number CN112083035A discloses a test device and test method for the thermal conductivity of a lithium-ion battery. This method is based on the transient method to test the thermal conductivity of a lithium-ion battery, which takes a long time and has no heat loss calibration process, making it difficult to accurately measure the thermal conductivity of the battery.

[0005] Therefore, how to provide a method for measuring the thermal conductivity in the thickness direction of an energy storage battery that is applicable not only to lithium-ion and sodium-ion energy storage batteries in the form of square, cylindrical, and soft-pack, but also to lithium-ion and sodium-ion power batteries of various shapes, and can quickly and accurately measure the thermal conductivity of the battery is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0006] In view of this, the present invention proposes a method for measuring the thermal conductivity in the thickness direction of an energy storage battery.

[0007] To achieve the above object, the present invention adopts the following technical solutions: A method for measuring the thermal conductivity in the thickness direction of an energy storage battery, comprising: Step 1: Perform constant power uniform heating on the two main surfaces of the two closely attached energy storage batteries at a first preset ambient temperature until the battery temperature reaches the first preset temperature, substitute the temperature difference between the cold and hot surface temperatures during the heating process and the first preset ambient temperature into a pre-set linear fitting equation of temperature difference and temperature drop rate, obtain the temperature drop rates of the cold and hot surfaces, and integrate them over the battery heating time to obtain the temperature drop amplitudes of the cold and hot surfaces caused by heat loss; wherein the hot surface is the main surface for constant power uniform heating, and the cold surface is the other main surface; Step 2: At a first preset ambient temperature, the symmetrical main surfaces of the two closely attached energy storage batteries are uniformly heated at constant power to obtain the temperatures of the cold and hot surfaces when the thermal field of the battery reaches a quasi-steady state, and based on the temperature drop amplitude of the cold and hot surfaces caused by heat loss, correction is performed to obtain the actual temperatures of the cold and hot surfaces of the energy storage battery during heating in a real environment; Step 3: Based on Fourier's law of heat conduction, the heat flux density is obtained, and the heat flux density is integrated in the thickness direction of the battery to obtain a theoretical model of the thermal conductivity coefficient in the thickness direction of the energy storage battery. The actual temperatures of the cold and hot surfaces of the energy storage battery in the actual environment are substituted to obtain the thermal conductivity coefficient in the thickness direction of the energy storage battery at the working temperature to be measured; wherein the working temperature to be measured is the average value of the first preset ambient temperature and the first preset temperature.

[0008] Optionally, the process of obtaining the pre-set linear fitting equation of temperature difference and temperature drop rate is specifically as follows: The energy storage battery is uniformly heated at a constant power at a second preset ambient temperature until the battery temperature reaches the second preset temperature, and the heating is stopped to record the temperature drop process of the energy storage battery; The temperature drop curve equation of the energy storage battery is fitted, the temperature drop rate is obtained by first-order derivative, and the temperature difference between the battery temperature and the second preset ambient temperature during the temperature drop process is calculated, and the temperature drop rate is fitted to obtain a linear fitting equation of the temperature difference and the temperature drop rate.

[0009] Optionally, the temperature drop process of the energy storage battery is a temperature drop process from the second preset temperature to below a third preset temperature; wherein the third preset temperature is the second preset ambient temperature plus 3°C.

[0010] Optionally, the initial temperature of the energy storage battery is equal to the ambient temperature.

[0011] Optionally, based on the temperature drop amplitude of the cold and hot surfaces caused by heat loss, correction is performed to obtain the actual temperature of the cold and hot surfaces of the energy storage battery during heating in a real environment, as follows: in, , They are the actual temperatures of the cold and hot surfaces of the energy storage battery during heating in a real environment; , are the cold and hot surface temperatures when the battery thermal field reaches a quasi-steady state, respectively; , are the temperature drops of the cold and hot surfaces caused by heat loss, respectively.

[0012] Optionally, the theoretical model of the thermal conductivity in the thickness direction of the energy storage battery is as follows: ; where is the thermal conductivity in the thickness direction of the energy storage battery; is the surface power density of the hot surface, with the unit of W / m 2 , and the calculation method is the input power of the heating film divided by the area of the battery heated surface, which is used to make the temperature difference between the cold and hot surfaces tend to be constant; are the actual temperatures of the cold and hot surfaces of the energy storage battery during the heating process in the real environment, respectively.

[0013] Optionally, by adjusting the first preset environmental temperature, the thermal conductivity in the thickness direction of the energy storage battery at different working temperatures to be measured can be obtained.

[0014] From the above technical solutions, it can be seen that compared with the prior art, the present invention proposes a method for measuring the thermal conductivity in the thickness direction of an energy storage battery. By considering the temperature drops of the cold and hot surfaces caused by heat loss when measuring the thermal conductivity in the thickness direction of the energy storage battery and correcting the temperatures of the cold and hot surfaces based on the temperature drops, the measurement accuracy of the thermal conductivity in the thickness direction is effectively improved compared with the ideal calculation model of the thermal conductivity in the prior art. By obtaining the cold and hot surface temperatures when the battery thermal field reaches a quasi-steady state based on the quasi-steady state theory of heat transfer to calculate the thermal conductivity in the thickness direction, the thermal conductivity of the battery can be measured in about 600 s. Compared with the steady state method or the conventional transient method, the test period is effectively reduced and the measurement speed is increased. And when conducting experiments, the present invention uses inexpensive thermal insulation materials to wrap the battery, and then uses an electric heating film to heat the battery at a constant power. Compared with using a hot wire or a hot disk thermal conductivity test instrument to test the thermal conductivity of the battery, it has a significant cost advantage. At the same time, the present invention is not only applicable to lithium-ion and sodium-ion batteries for energy storage in the form of square, cylindrical, and soft packages, but also applicable to lithium-ion and sodium-ion batteries for power with various shapes, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to the provided drawings without creative efforts.

[0016] Figure 1 This is a schematic diagram of the method flow of the present invention.

[0017] Figure 2 This is a schematic diagram of the two-dimensional structure of two closely attached energy storage batteries of the present invention.

[0018] Figure 3 This is a schematic diagram of the temperature change of the energy storage battery of the present invention when heated at the first preset ambient temperature.

[0019] Figure 4 This is a schematic diagram of the curve equation of the battery temperature of the present invention over time.

[0020] Figure 5 This is a schematic diagram of the temperature drop of the energy storage battery of the present invention at the second preset ambient temperature.

[0021] Figure 6 This is a schematic diagram of the fitting curve of the thermal conductivity in the thickness direction of the energy storage battery measured by the present invention at different working temperatures to be measured.

[0022] Among them, 1 - electric heating film, 2 - thermocouple, 3 - battery inner core, 4 - battery outer shell. Specific embodiments

[0023] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0024] Embodiment 1: Embodiment 1 of the present invention discloses a method for measuring the thermal conductivity in the thickness direction of an energy storage battery, as Figure 1 shown, including: In the implementation of the present invention, a soft-pack lithium iron phosphate battery is selected as the energy storage battery, with dimensions, mass, and capacity of 11×80×130 mm3, 235 g, and 9.0 Ah respectively; the battery is insulated with a silica aerogel felt with a thickness of 10 mm, and then placed statically in a vacuum chamber, and the air pressure in the vacuum chamber is adjusted to -90 kPa; a thermocouple 2 is arranged at each of the hot and cold surfaces of the energy storage battery, and the thermocouple 2 is respectively arranged at the center positions of the hot and cold surfaces of the battery, and the thermocouple 2 is externally connected to a temperature data acquisition instrument; the battery SOC is 50%, and the ambient temperature and the initial temperature of the battery are provided by a high and low temperature test chamber; the heating of the energy storage battery is provided by an electrothermal film 1, a laser heater, or an electromagnetic heater; the size of the electrothermal film 1 used is 0.2×80×130 mm3, the mass is 2.0 g, and the heating power is not higher than 1% affected by temperature, and a constant input power is provided by a high-precision DC regulated power supply; the maximum temperature of the battery is not higher than 80°C.

[0025] Regarding the energy storage battery as a homogeneous entity, the main surface for constant power uniform heating is the hot surface (heated surface), and the other main surface is the cold surface (adiabatic surface). The four small side surfaces of each battery are adiabatic surfaces, and one-dimensional heat conduction (transient) occurs in the thickness direction.

[0026] Step 1: At the first preset ambient temperature of -30°C, perform constant power uniform heating of 20.0 W on the two outer main surfaces of the two tightly attached energy storage batteries as shown in Figure 2 until the battery temperature reaches the first preset temperature of -10°C. The temperature change of the energy storage battery when heated at the first preset ambient temperature is as shown in Figure 3 , where TC1, TC2, and TC3 are thermocouples 2, is the ambient temperature, which is the first preset ambient temperature here; substitute the temperature differences and between the cold and hot surface temperatures and the first preset ambient temperature during the heating process into the pre-set linear fitting equation of the temperature difference and the temperature drop rate to obtain the temperature drop rates of the cold and hot surfaces, and integrate over the battery heating time to obtain the temperature drop amplitudes and caused by heat loss of the cold and hot surfaces (take positive values). Figure 2 The two tightly attached energy storage batteries in

[0027] include: an electrothermal film 1, a thermocouple 2, a battery inner core 3, and a battery outer shell 4. As shown in Figure 4 , the curve equation of the battery temperature with respect to time can be fitted. Take the first derivative of this equation to get , and let it be In addition, from Figure 4 it is also known that:

[0028] This formula defines to the difference relationship of the temperature change amount within the time period; According to the law of conservation of energy, it can be known that:

[0029] Among them, the left side of the equation is the reduction amount of the battery's own thermal energy when the battery temperature drops by a certain amplitude, and the right side of the equation is the reduction amount of the battery's thermal energy within the time ; is the battery mass, is the specific heat capacity of the battery; For an object with a mass of and a specific heat capacity of , the heat change caused by the temperature change ; is the temperature change rate ( the first-order derivative of to ), and its integral reflects the relationship between the heat change and the integral of the temperature change rate; Analyze the extreme case as follows: When is long enough, , at this time:

[0030] Among them, is the relationship between the battery temperature drop rate and time, is a constant. From this formula, it can be known that the difference between the battery temperature and the initial temperature (ambient temperature) is linearly related to its own temperature drop rate.

[0031] The process of obtaining the linear fitting equation of the preset temperature difference and the temperature drop rate is specifically as follows: Under the second preset ambient temperature of 0°C, use a heater to heat the energy storage battery at a constant power of 20.0W until the battery temperature reaches the second preset temperature of 41°C, and stop heating and record the temperature drop process of the energy storage battery. As Figure 5 shown, where is the average battery temperature, is the ambient temperature, which is the second preset ambient temperature here; Fit the temperature drop curve equation of the energy storage battery , take the first-order derivative to obtain the temperature drop rate , and calculate the temperature difference between the battery temperature and the second preset ambient temperature during the temperature drop process , and the temperature drop rate are fitted to obtain the linear fitting equation of temperature difference and temperature drop rate: .

[0032] The temperature drop process of the energy storage battery is a temperature drop process from the second preset temperature to below the third preset temperature; wherein the third preset temperature is the second preset ambient temperature plus 3°C, and in the embodiment of the present invention, the third preset temperature is 5°C.

[0033] The initial temperature of the energy storage battery is equal to the ambient temperature.

[0034] Step 2: At the first preset ambient temperature of -30°C, the symmetrical main surfaces (non-contact) of the two closely attached energy storage batteries are uniformly heated at a constant power of 20.0W to obtain the cold and hot surface temperatures when the battery thermal field reaches a quasi-steady state. and , and based on the temperature drop of the cold and hot surfaces caused by heat loss and Correction is made to obtain the actual temperature of the cold and hot surfaces of the energy storage battery during heating in a real environment and .

[0035] Based on the temperature drop caused by heat loss on the cold and hot surfaces, the actual temperature of the cold and hot surfaces of the energy storage battery in the actual environment is obtained as follows: in, , They are the actual temperatures of the cold and hot surfaces of the energy storage battery during heating in a real environment; , are the cold and hot surface temperatures when the battery thermal field reaches a quasi-steady state; , are the temperature drop amplitudes caused by heat loss on the cold and hot surfaces respectively.

[0036] Step 3: Calculate the heat flux density based on Fourier's law of heat conduction , and integrate the heat flux density in the thickness direction of the battery to obtain the theoretical model of the thermal conductivity coefficient in the thickness direction of the energy storage battery, substitute the actual temperatures of the cold and hot surfaces of the energy storage battery in the actual environment during heating, and obtain the thermal conductivity coefficient in the thickness direction of the energy storage battery at the working temperature to be measured; wherein the working temperature to be measured is the average value of the first preset ambient temperature and the first preset temperature.

[0037] The theoretical model of thermal conductivity in the thickness direction of energy storage batteries is as follows: ; in, is the thermal conductivity of the energy storage battery in the thickness direction; is the surface power density of the hot surface, in W / m 2 , calculated by dividing the input power of the heating film by the heating surface area of the battery, is used to make the temperature difference between the cold and hot surfaces tend to be constant; , They are respectively the actual temperatures of the cold and hot surfaces of the energy storage battery during heating in a real environment.

[0038] The thermal conductivity measured under the working conditions of the embodiment of the present invention is the thermal conductivity of the energy storage battery in the thickness direction at the working temperature to be measured -20°C (the average value of the initial temperature of the battery and the maximum temperature when heating is stopped, that is, the average value of the first preset ambient temperature and the first preset temperature). By adjusting the first preset ambient temperature, the thermal conductivity of the energy storage battery in the thickness direction at different working temperatures to be measured can be obtained, such as Figure 6 shown.

[0039] The embodiment of the present invention discloses a method for measuring the thermal conductivity in the thickness direction of an energy storage battery. The present invention considers the temperature drop caused by heat loss on the cold and hot surfaces when measuring the thermal conductivity in the thickness direction of the energy storage battery, and corrects the temperature of the cold and hot surfaces based on the temperature drop. Compared with the ideal calculation model of thermal conductivity in the prior art, the measurement accuracy of the thermal conductivity in the thickness direction is effectively improved. The present invention obtains the temperature of the cold and hot surfaces when the battery thermal field reaches a quasi-steady state based on the quasi-steady-state theory of heat transfer to calculate the thermal conductivity in the thickness direction, and can measure the thermal conductivity of the battery in about 600s. Compared with the steady-state method or the conventional transient method, the test cycle is effectively reduced and the measurement speed is improved. In addition, the present invention uses cheap insulation materials to cover the battery during the experiment, and then uses an electric heating film to heat the battery at constant power. Compared with using a hot wire or hot plate thermal conductivity test instrument to test the thermal conductivity of the battery, it has a significant cost advantage. At the same time, the present invention is not only applicable to lithium-ion and sodium-ion batteries for energy storage in square, cylindrical, and soft-pack forms, but also to lithium-ion and sodium-ion batteries for power of various shapes.

[0040] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0041] The foregoing description of the disclosed embodiments enables those skilled in the art to practice or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for measuring the thermal conductivity in the thickness direction of an energy storage battery, characterized in that include: Step 1: Performing constant power uniform heating on the two main surfaces of the two closely attached energy storage batteries at a first preset ambient temperature until the battery temperature reaches the first preset temperature, substituting the temperature difference between the cold and hot surface temperatures during the heating process and the first preset ambient temperature into a pre-set linear fitting equation of the temperature difference and the temperature drop rate to obtain the temperature drop rates of the cold and hot surfaces, and integrating them over the battery heating time to obtain the temperature drop amplitudes of the cold and hot surfaces caused by heat loss; wherein the hot surface is the main surface subjected to the constant power uniform heating, and the cold surface is the other main surface; Step 2: uniformly heat the symmetrical main surfaces of two closely attached energy storage batteries at a constant power at a first preset ambient temperature, obtain the temperatures of the cold and hot surfaces when the thermal field of the battery reaches a quasi-steady state, and make corrections based on the temperature drop amplitudes of the cold and hot surfaces caused by heat loss, to obtain the actual temperatures of the cold and hot surfaces of the energy storage battery during heating in a real environment; Step 3: Based on Fourier's law of heat conduction, the heat flux density is obtained, and the heat flux density is integrated in the thickness direction of the battery to obtain a theoretical model of the thermal conductivity coefficient in the thickness direction of the energy storage battery, and the actual temperatures of the cold and hot surfaces of the energy storage battery in the actual environment are substituted to obtain the thermal conductivity coefficient in the thickness direction of the energy storage battery at the working temperature to be measured; wherein the working temperature to be measured is the average value of the first preset ambient temperature and the first preset temperature.

2. The method for measuring the thermal conductivity in the thickness direction of an energy storage battery according to claim 1, wherein The process of obtaining the preset linear fitting equation of the temperature difference and the temperature drop rate is specifically as follows: The energy storage battery is uniformly heated at a constant power at a second preset ambient temperature until the battery temperature reaches the second preset temperature, and the heating is stopped to record the temperature drop process of the energy storage battery; The temperature drop curve equation of the energy storage battery is fitted, the temperature drop rate is obtained by first-order derivative, and the temperature difference between the battery temperature and the second preset ambient temperature during the temperature drop process is calculated, and the temperature drop rate is fitted to obtain a linear fitting equation of the temperature difference and the temperature drop rate.

3. A method for measuring the thermal conductivity in the thickness direction of an energy storage battery according to claim 2, characterized in that, The temperature drop process of the energy storage battery is a temperature drop process in which the second preset temperature drops to below a third preset temperature; wherein the third preset temperature is the second preset ambient temperature plus 3°C.

4. A method for measuring the thermal conductivity in the thickness direction of an energy storage battery according to claim 2, characterized in that, The initial temperature of the energy storage battery is equal to the ambient temperature.

5. A method for measuring the thermal conductivity in the thickness direction of an energy storage battery according to claim 1, characterized in that, Based on the temperature drop amplitude of the cold and hot surfaces caused by heat loss, the actual temperature of the cold and hot surfaces of the energy storage battery in the actual environment is obtained as follows: wherein, and are respectively the actual temperatures of the cold and hot surfaces of the energy storage battery during the heating process in the real environment; and are respectively the cold and hot surface temperatures when the battery thermal field reaches a quasi-steady state; and are respectively the temperature drop amplitudes of the cold and hot surfaces caused by heat loss.

6. A method for measuring the thermal conductivity in the thickness direction of an energy storage battery according to claim 1, characterized in that The theoretical model of thermal conductivity in the thickness direction of the energy storage battery is as follows: ； Among them, is the thermal conductivity in the thickness direction of the energy storage battery; is the surface power density of the hot surface, and the unit is W / m 2 , and the calculation method is the input power of the heating film divided by the area of the battery's heated surface, which is used to make the temperature difference between the cold and hot surfaces tend to be constant; , are the actual temperatures of the cold and hot surfaces of the energy storage battery during the heating process in the actual environment, respectively.

7. A method for measuring the thermal conductivity in the thickness direction of an energy storage battery according to claim 1, characterized in that, The first preset ambient temperature is adjusted to obtain the thermal conductivity coefficient in the thickness direction of the energy storage battery at different working temperatures to be measured.

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