Method and device for measuring radial heat conductivity and specific heat of cylindrical battery

Abstract

This invention discloses a method and apparatus for measuring the radial thermal conductivity and specific heat of a cylindrical battery. The apparatus includes a temperature control chamber, a battery pack placed inside the chamber, a heating component for heating, and a data acquisition and processing unit for measuring the battery pack. This invention maintains a high and constant level of heat flow into the battery by heating the side of the battery under test and providing uniform thermal protection, while controlling the heat loss rate at a low and constant level. The radial thermal conductivity and specific heat of the cylindrical battery are then calculated based on the transient temperature rise characteristics of the battery's outer surface. This invention enables non-destructive in-situ measurement of the radial thermal conductivity and specific heat of cylindrical batteries. It can be used to measure the radial thermal conductivity and specific heat of cylindrical batteries under different temperature conditions, with short testing time, high accuracy, ease of implementation, and low cost.

Description

Technical Field

[0001] This invention relates to the field of thermal property parameter research and thermal management technology of energy storage batteries, and in particular to a method and apparatus for measuring the radial thermal conductivity and specific heat of cylindrical batteries. Background Technology

[0002] Lithium-ion batteries are now widely used in electric vehicles, but there are still many problems in terms of thermal safety and thermal characteristics. For example, excessively high battery temperature affects battery reliability and safety, and temperature unevenness seriously affects battery life. The thermal safety and temperature of the battery are closely related to the battery's thermal conductivity.

[0003] Thermal conductivity is a crucial parameter affecting temperature uniformity in batteries, reflecting their thermal conductivity. Specific heat, a physical quantity representing the thermal properties of a material, reflects the battery's ability to absorb and release heat per unit time. Changes in these thermal properties can lead to significant variations in the battery's temperature gradient. Accurately measuring the thermal conductivity and specific heat of lithium-ion batteries is indispensable for accurately estimating their thermal behavior and preventing thermal runaway.

[0004] To address the aforementioned issues, patent document No. 201910641508.2 discloses a method for testing the specific heat capacity and radial thermal conductivity of a cylindrical power battery. This method involves establishing a theoretical model for the specific heat capacity and radial thermal conductivity of the cylindrical power battery under adiabatic conditions; recording the temperature change of the cylindrical power battery over time to calibrate its heat loss; and optimizing the theoretical model in step S1 based on the results of step S2 to obtain a model for the specific heat capacity and radial thermal conductivity of the cylindrical power battery under non-adiabatic conditions, followed by experimental testing.

[0005] The theoretical calculation model for the specific heat capacity and radial thermal conductivity of a cylindrical power battery established in this patent application takes into account the influence of heat loss, and has higher testing accuracy compared to traditional methods that do not consider heat loss when measuring the battery's thermal properties. However, the overall experimental time is long and requires disassembling the battery, which is a destructive measurement.

[0006] In addition, an invention patent application with application number 202210667344.2 discloses a battery spread thermal conductivity testing device and method. The device includes a high and low temperature test chamber and multiple batteries to be tested placed inside the high and low temperature test chamber. At least two of the batteries to be tested have built-in thermocouples. A heating film is attached to one side of each battery to be tested. All the batteries to be tested are arranged in pairs in the high and low temperature test chamber with the sides with heating films facing each other. The battery to be tested with built-in thermocouples is located in the middle of the high and low temperature test chamber and its heating film has a thermocouple attached. The non-heating film side of the battery to be tested with built-in thermocouples also has a thermocouple attached. The surfaces of the batteries to be tested that are in contact with the chamber are covered with thermal insulation material. All heating films are connected in parallel and connected to a DC power supply. All thermocouples are connected to a data logger.

[0007] This method can actually measure the battery's internal temperature, rather than the temperature of the metal casing, thus obtaining accurate data and avoiding the influence of the metal casing. Overall, the thermal conductivity obtained by this method is closer to the actual battery temperature, resulting in relatively accurate test results. However, this method also requires disassembling the battery; it is not a direct measurement.

[0008] Therefore, it is necessary to improve such a structure to overcome the aforementioned defects. Summary of the Invention

[0009] The purpose of this invention is to provide a method and apparatus for measuring the radial thermal conductivity and specific heat of cylindrical batteries, which can realize in-situ non-destructive measurement of cylindrical batteries, making the measurement results more realistic and accurate.

[0010] The above-mentioned technical objective of the present invention is achieved through the following technical solution:

[0011] A method for determining the radial thermal conductivity and specific heat of a cylindrical battery includes the following steps:

[0012] S1. With the battery under test as the center, a number of thermal protection batteries are arranged around it. The battery under test and the number of thermal protection batteries are connected by an insulating collar bracket to form a battery pack. A thermocouple of the battery under test is arranged at the upper, middle and lower ends of the side of the battery under test. A thermocouple of the thermal protection battery is arranged on the surface of one of the thermal protection batteries.

[0013] S2. A thin film heater is provided on the side of both the battery under test and the thermal protection battery, and a heat flow meter is provided outside the thin film heater of the battery under test. Then, a high thermal conductivity graphite sheet is provided between the thin film heater and the corresponding battery under test or thermal protection battery. The high thermal conductivity graphite sheet is used to balance the heat flow entering the battery.

[0014] S3. The top, sides and bottom of the battery pack are covered with heat-insulating felt to form a test section; then the battery pack is placed in a temperature control chamber, and the positive and negative wires of the thin film heater are connected to the DC power supply outside the temperature control chamber to provide a high level of constant heating power to the battery under test and control the heat loss rate at a low level of constant value.

[0015] S4. A temperature control box thermocouple is installed in the temperature control box to monitor the temperature inside the box, and the thermocouple of the battery under test, the thermocouple of the thermal protection battery, and the temperature control box thermocouple are connected to a data acquisition instrument to output temperature and voltage signals.

[0016] S5. Keep the temperature of the temperature control chamber constant at the initial temperature. After the battery temperature and the temperature inside the chamber reach thermal equilibrium, heat the battery under test and the thermal protection battery through the thin film heater, and record the change in the side temperature of the battery under test. Stop heating 100-800 seconds after heating to the quasi-steady state.

[0017] Let the length of the battery under test be H, the radius be r, the base area be A, the density be ρ, and the radial thermal conductivity be k. r The heating power of the thin-film heater is Q, and the average heating heat flux density on the side of the battery is q = Q / (πDH) - q loss , where q loss Let be the average heat flux density lost at the outer surface, and ΔT be the average temperature rise on the side of the battery. Then, the specific heat c of the battery can be expressed by the temperature rise rate dT / dt at the quasi-steady state as:

[0018]

[0019] The radial thermal conductivity k r It can be represented by temperature rise ΔT, battery specific heat c, radius r, and heat flux q:

[0020]

[0021]

[0022] Among them, Fourier number

[0023] Furthermore, this includes the following steps:

[0024] X1. Based on steps S1-S5, obtain the battery's temperature rise curve and the average heat flux density q of the external surface loss. loss Thus, we obtain q and the temperature rise ΔT = ΔT1(t);

[0025] X2. Calculate the battery specific heat c and instantaneous thermal conductivity k using the above formula. r1 and transient variable Fo1=kr1t / (ρcr 2The curve relationship between kr and kr1(Fo1) is kr = kr1(Fo1), k r1 Covers the range of measured thermal conductivity;

[0026] X3. The obtained instantaneous thermal conductivity k r1 Divide the time range into 5-10 equal parts, based on each k r1 Based on the specific heat c and the constant heat flux boundary condition q, a single-cell thermal model is established for transient numerical simulation. The thermal conductivity k is input separately. r1 And obtain the temperature rise ΔT = ΔT2 corresponding to the same time period t;

[0027] X4. For each input thermal conductivity k r1 In the simulation scenario, based on the temperature rise ΔT2 and t from the numerical simulation, the above k... r The corresponding thermal conductivity k can be obtained by formula. r2 (t) and divide it equally, k r2 (t) Equal division of time range and k r1 (t) are the same;

[0028] X5. Based on the simulated instantaneous thermal conductivity k r2 (t) Calculate the relative Fo2 = kr2t / (ρcr) 2 Plot the thermal conductivity k at the same time t with Fo2(t) as the horizontal axis. r1 With thermal conductivity k r2 (t) The relationship curve between the deviation of the two and Fo2, and the range of Fourier numbers Fo2 corresponding to the determined minimum deviation interval;

[0029] X6. Substitute k according to the determined range of Fo2. r Formula k r =k r1 (Fo) Back-calculate the corresponding thermal conductivity k r Range, taking k r The average value is the thermal conductivity to be measured.

[0030] Furthermore, in step S1, the battery under test and the thermal protection battery have similar radial thermal conductivity, and all thin-film heaters have the same heating power. The thermal insulation ring support structure is a cylinder with a hollowed-out section in the middle to accommodate the batteries, and the gaps between the batteries are filled with thermal insulation felt material.

[0031] Furthermore, in step S1, the outer insulating film of the battery under test is peeled off to reduce the contact thermal resistance and measurement error caused by the outer insulating film.

[0032] Furthermore, in step S2, the high thermal conductivity graphite sheet is selected as a thin graphite sheet with a high thermal conductivity coefficient to facilitate temperature equalization of the battery; the heat flow meter should be set outside the thin film heater, and the position of the heat flow meter should be staggered from the positions of the thermocouple of the battery under test and the thermocouple of the thermal protection battery.

[0033] Furthermore, in step S2, the thin-film heater and the heat flow meter are fixed with nylon cable ties to reduce the gap between the thin-film heater and the heat flow meter and the battery. A layer of thermally conductive silicone grease is uniformly applied between the thin-film heater and the heat flow meter to reduce measurement errors caused by contact.

[0034] Furthermore, the insulating felt in step S3 is silica aerogel.

[0035] Furthermore, in step S5, the battery under test and the thermal protection battery are connected to the same device as the power line leading out from the battery under test to ensure the consistency of battery heating time.

[0036] Furthermore, in step S5, based on the experimentally measured specific heat and the heating power provided by the DC power supply, numerical simulations are performed for the thermal conductivity values ​​ranging from 0 to the maximum possible thermal conductivity. The optimal data range for the experiment when the thermal conductivity values ​​are between 0 and the maximum possible thermal conductivity is determined by the numerical simulation. The maximum possible thermal conductivity is calculated by summing the series thermal resistances of the battery's electrode materials and casing materials, which is 1.4 W / m·K in this case. Due to interlayer contact thermal resistance, such as the contact thermal resistance between the positive electrode and the separator, and the contact thermal resistance between the separator and the negative electrode material, the actual thermal conductivity is less than the maximum possible thermal conductivity.

[0037] A device for measuring the radial thermal conductivity and specific heat of a cylindrical battery includes a temperature control chamber, a battery pack placed inside the temperature control chamber, a heating component for heating, and a data acquisition and processing unit for measuring the battery pack.

[0038] The battery pack includes several cylindrical batteries. Each cylindrical battery includes a test battery located at the center and several thermal protection batteries arranged around the test battery. The test battery and the several thermal protection batteries are connected and fixed by an insulating collar bracket. The cylindrical batteries and the insulating collar bracket are covered with an insulating felt.

[0039] The heating assembly includes a thin-film heater disposed on the side of the cylindrical battery, a high thermal conductivity graphite sheet disposed between the thin-film heater and the cylindrical battery, the high thermal conductivity graphite sheet being used to balance the heat flow entering the battery, and a heat flow meter disposed outside the thin-film heater of the battery under test, the thin-film heater and the heat flow meter being connected to a DC power supply through the thin-film heater wire and the heat flow meter wire, respectively.

[0040] The data acquisition and processing unit includes several thermocouples. One end of each thermocouple is used to detect the temperature and voltage of the upper, middle, and lower ends of the side of the battery under test, the side temperature and voltage of one of the several thermal protection batteries, and the temperature and voltage inside the temperature control box. The other end of each thermocouple is connected to a data acquisition instrument, and a computer is connected to and controls the data acquisition instrument.

[0041] In summary, the present invention has the following beneficial effects:

[0042] 1. The method for measuring the radial thermal conductivity and specific heat of a cylindrical battery of the present invention overcomes the shortcomings of existing technologies that cannot measure the radial thermal conductivity in situ without damage. By arranging the battery reasonably, an approximately constant heat flow environment is created for the battery under test. The battery is heated from the side without damaging it. The temperature rise during the heating process is monitored by thermocouples arranged at the upper, center and lower ends of the side of the battery. At the same time, the heat loss of the battery is monitored by heat flow meters arranged on the side of the battery under test. The radial thermal conductivity and specific heat of the cylindrical battery can be measured directly and accurately, simplifying the thermal parameter measurement steps.

[0043] 2. The method for measuring the radial thermal conductivity and specific heat of a cylindrical battery of the present invention determines the minimum deviation range of Fo through deviation analysis, thereby obtaining a more accurate radial thermal conductivity.

[0044] 3. The measuring device of the present invention is simple, easy to purchase, and easy to operate. By adjusting the initial temperature of the temperature control chamber and repeating the measurement process, it can test the radial thermal conductivity of cylindrical batteries under different temperature conditions. It can provide reliable radial thermal conductivity and specific heat test data of cylindrical batteries for cylindrical battery manufacturers, electric vehicle companies and other institutions. It is suitable for cylindrical batteries of various sizes, has strong adaptability, and can provide thermal parameter data for battery thermal management and thermal runaway protection design.

[0045] 4. This invention combines experiments with a simple simulation model to determine the radial thermal conductivity. Although cylindrical batteries have several standard sizes, such as 18650, 21700, and 4680, and the battery materials differ for each size, one simulation model is suitable for batteries of the same standard size. For batteries of the same size but different materials, the same simulation model can be used without reconstruction. Furthermore, the number of meshes is small, the simulation calculation time is short, and it can be completed within minutes. The data volume is small and can be pre-stored in a database, thus ensuring that deviation calculations are performed in real time to obtain the Fourier number corresponding to the minimum deviation interval, achieving rapid measurement at low cost. This provides a new method for measuring thermal properties parameters such as the radial thermal conductivity of batteries. Attached Figure Description

[0046] Figure 1 This is a flowchart of the present invention.

[0047] Figure 2This is a schematic diagram of the cylindrical battery pack of the present invention.

[0048] Figure 3 This is a schematic diagram of the heat-insulating collar bracket used to fix the battery and the thin-film heater in this invention.

[0049] Figure 4 This is a cross-sectional view of the cylindrical battery pack structure of the present invention.

[0050] Figure 5 This is a schematic diagram of the device for measuring the radial thermal conductivity and specific heat of a cylindrical battery in this invention.

[0051] Figure 6 The thermal conductivity k of the cylindrical battery under test is obtained from step X2. r1 Curve relationship with Fo1

[0052] Figure 7 This is a graph showing the relationship between the heat flow on the side of the cylindrical battery under test and time, according to an embodiment of the present invention.

[0053] Figure 8 This is a graph showing the relationship between the side temperature rise of the cylindrical battery under test and time, according to an embodiment of the present invention.

[0054] Figure 9 This is a graph showing the deviation between the numerical simulation value of thermal conductivity and the input value obtained by numerical simulation based on the actual measured heat flow condition q and specific heat c in this embodiment of the present invention.

[0055] Figure 10 This is a comparison chart showing the temperature results of single-cell numerical simulation based on thermal conductivity and specific heat obtained from the implementation examples of this invention, and the deviation comparison chart. Detailed Implementation

[0056] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to the figures and specific embodiments.

[0057] See Figures 1-10 The present invention proposes S1, placing the cylindrical battery to be tested at the center as the battery to be tested, and distributing multiple other batteries of the same or similar specifications at the same height around the battery to be tested, forming a thermal protection battery. A thermocouple is welded to the upper, center and lower end of the side of the battery to be tested to monitor the side temperature of the battery to be tested, and a monitoring thermocouple is welded to one of the surrounding batteries. The battery to be tested and the surrounding thermal protection batteries are fixed by two thermally insulating ring brackets to form a battery pack.

[0058] S2. Apply a thin-film heater to the side of each battery, covering more than 80% of the battery side area. Then, attach a high thermal conductivity graphite sheet of the same size as the battery side between the battery side and the thin-film heater to balance the heat flow into the battery. Apply the thin-film heater to the side of each battery and attach a heat flow meter to the outside of the thin-film heater of the battery under test. Use thermal insulation tape and nylon cable ties to fix the heat flow meter to the outside of the thin-film heater of the battery under test. Lead the wires of the thin-film heater downwards.

[0059] S3. Wrap the sides of the battery pack completely with heat-insulating felt, and cover the top and bottom with heat-insulating felt of the same thickness to form a test section. Then place the battery pack inside the temperature control chamber, connect the positive and negative wires of the thin film heater to the DC power supply outside the temperature control chamber, provide constant heating power to the battery under test, and control the heat loss rate at a low constant value.

[0060] S4. Arrange thermocouples for monitoring the temperature inside the temperature control box, and connect the thermocouples for monitoring the battery temperature, the thermocouples for monitoring the temperature inside the box, and the thermocouples for monitoring the battery under test at the center of the heat flow meter to the data acquisition instrument to output temperature and voltage signals.

[0061] S5. Control the temperature control box to maintain the temperature inside the box at a constant initial temperature. The battery pack is placed in the box to eliminate the inconsistency between the battery pack temperature and the set temperature. The upper and lower covers of the insulating felt can also be opened to accelerate the temperature equalization process. When the battery temperature and the temperature inside the box reach thermal equilibrium, that is, the temperature change is within 0.2℃ for 5 consecutive minutes, the cylindrical battery is heated by the thin film heater. The thin film heaters of the surrounding thermal protection batteries are connected in series, and the thin film heater of the central battery under test is controlled separately. The temperature change on the side of the battery under test is recorded. Heating is stopped after 200-800 seconds. Note that the heating temperature rise must be controlled within the safe temperature range of the battery, such as the battery temperature not exceeding 60℃.

[0062] Let the length of the battery under test be H, the radius be r, the base area be A, the density be ρ, and the radial thermal conductivity be k. r The heating power of the thin-film heater is Q, and the average heating heat flux density on the side of the battery is q = Q / (πDH) - q loss , where q loss Let be the average heat flux density lost on the outer surface, and ΔT be the average temperature rise on the side of the battery. Then, the specific heat c of the battery can be expressed by the temperature rise rate dT / dt during the quasi-steady-state stage, i.e., the stage where the temperature of the battery under test rises steadily at almost the same rate:

[0063]

[0064] The radial thermal conductivity k r It can be represented by temperature rise ΔT, battery specific heat c, radius r, and heat flux q:

[0065]

[0066]

[0067] Among them, F O =krt / ρcr 2 .

[0068] S6. The battery will stop heating after 600 seconds to allow it to cool down naturally.

[0069] The specific heat value c is obtained by measuring the measured battery heating power q and the temperature rise rate dT / dt, and then the radial thermal conductivity is determined according to steps X1-X6.

[0070] X1. Based on steps S1-S5, obtain the battery's temperature rise curve and the average heat flux density q of the external surface loss. loss Thus, we obtain q and the temperature rise ΔT = ΔT1(t);

[0071] X2. Based on the above formula and the temperature rise during the steady-state phase of the battery under test (i.e., the quasi-steady-state phase), the specific heat c and the instantaneous thermal conductivity k of the battery are obtained. r1 and transient variable Fo1=kr1t / (ρcr 2 The curve relationship between kr and kr1(Fo1) is kr = kr1(Fo1), k r1 Covers the range of measured thermal conductivity; Figure 6 To determine the appropriate Fo1 value in order to establish the curve relationship kr = kr1(Fo1) between the thermal conductivity of the cylindrical battery under test and the variable Fo1 obtained in this embodiment of the invention, the following steps are required. r1 .

[0072] X3. The obtained instantaneous thermal conductivity k r1 Divide the time range into 5-10 equal parts, based on each k r1 Based on the specific heat c and the constant heat flux boundary condition q, a single-cell thermal model is established for transient numerical simulation. The thermal conductivity k is input separately. r1 And obtain the temperature rise ΔT = ΔT2 corresponding to the same time period t;

[0073] X4. For each input thermal conductivity k r1 In the simulation scenario, based on the temperature rise ΔT2 and t from the numerical simulation, the above k... r The corresponding thermal conductivity k can be obtained by formula. r2 (t) and divide it equally, k r2 (t) Equal division of time range and k r1 (t) are the same;

[0074] X5. Based on the simulated instantaneous thermal conductivity kr2 (t) Calculate the relative Fo2 = kr2t / (ρcr) 2 Plot the thermal conductivity k at the same time t with Fo2(t) as the horizontal axis. r1 With thermal conductivity k r2 (t) The relationship curve between the deviation of the two and Fo2, and the range of Fourier numbers Fo2 corresponding to the determined minimum deviation interval;

[0075] X6. Substitute k according to the determined range of Fo2. r Formula k r =k r1 (Fo) Back-calculate the corresponding thermal conductivity k r Range, taking k r The average value is the thermal conductivity to be measured.

[0076] Figure 7 The graph shows the relationship between heat flow loss on the side of the cylindrical battery under test and time, obtained from an embodiment of the present invention. The q in the above formula can be obtained by subtracting the heat flow loss from the total heat flow. Figure 8 This is a graph showing the relationship between the side temperature rise of the cylindrical battery under test and time, obtained from an embodiment of the present invention. Figure 9 The present invention uses numerical simulation based on the heating power q and the measured specific heat in this embodiment to obtain the temperature rise, thereby obtaining the deviation diagram between the simulated thermal conductivity value and the simulated input value.

[0077] The specific measurement steps are as follows: (1) After the experimental measuring device is assembled (0% SOC), the initial experimental temperature is set to 20℃, the heating power of a single battery is 1.94W, and the heating is stopped after 600s under natural convection conditions, allowing it to cool down naturally (take the average temperature of the three thermocouples on the side of the battery as the battery side temperature, and take the average temperature of the three thermocouples on the side of the battery before heating as the battery initial temperature, and measure the battery side temperature rise rate during the basically unchanged period of time through the experiment). Figure 8 The temperature rise rate was obtained by linear fitting from 100s to 300s. The average input heat flux q corresponding to 100s to 300s was 472W / m. 2 The fitted temperature rise rate is 0.0371℃ / s, and the specific heat of the battery under test is 1043J / (kg·K) obtained from the temperature rise rate.

[0078] (2) Based on the experimental input heat flux of 472 W / m 2 (Power 1.94W), specific heat 1043J / (kg·K), numerical simulation analysis of the experimental setup was performed for the battery with different input thermal conductivity kr1. The input thermal conductivity kr1 at the same time was plotted with Fo2(t) as the horizontal axis. r1 With the simulated thermal conductivity k r2(t) The relationship curves between the deviations of the two and Fo2 ( Figure 9 To determine the minimum deviation range, the results show that when the thermal conductivity is between 0 and 1.4 W / m·K, F O The relative deviations between the numerical settings and simulation input values ​​corresponding to 0.236–0.266 are all below 3–5% (F O =kt / ρcr 2 (where k is the calculated value), take F O The average thermal conductivity value corresponding to 0.236 to 0.266 was used as the measured thermal conductivity value. The average radial thermal conductivity of the battery was found to be 1.181 W / m·K. The relative deviation was within 3-5%, indicating that this data range has good accuracy and reliability in providing thermal conductivity results. In other words, F... O =0.236~0.266 corresponds to the time period of 44~54s, which is the optimal fitting time period. At this time, the relative deviation between the thermal conductivity set by the simulation model and the thermal conductivity calculated by formula (2) is the smallest.

[0079] Figure 10 The graph shows the absolute value of the difference between the simulated and experimental temperature rise on the side of the battery as a function of thermal conductivity. The horizontal axis represents the assumed thermal conductivity value, and the vertical axis represents the absolute value of the difference between the simulated and experimental temperature rise at the optimal time (the time when the relative deviation between the different thermal conductivity values ​​and the calculated values ​​is the smallest). The results show that the temperature difference between the experiment and the simulation is the smallest when the thermal conductivity is set to 1.181 W / m·K at the corresponding optimal time. This further proves the accuracy of the radial thermal conductivity value measured in this experiment, meets the engineering accuracy requirements, and verifies the reliability of this measurement method. (Note: In (2), the thermal conductivity value should be set based on the specific experimental measurement range to determine the numerical simulation range. The optimal time period is different for different types of cylindrical batteries. This method simulated cylindrical batteries of sizes 18650, 21700, and 26650 within the range of thermal conductivity of 0 to 1.4 W / m·K. The relative deviation between the thermal conductivity value and the calculated value within 3 to 5% has a corresponding F. o But the corresponding F o The specific optimal time period varies, therefore it should be determined based on the specific parameters of the experimental battery. This invention only provides the test method and test device.

[0080] The present invention provides a method and apparatus for measuring the radial thermal conductivity and specific heat of cylindrical batteries. It can test the radial thermal conductivity and specific heat of cylindrical batteries under different temperature conditions. The test time is short, the results are accurate, the cost is low and it is easy to implement. It can provide reliable axial thermal conductivity of cylindrical batteries for cylindrical battery manufacturers, electric vehicle companies, research institutes and other institutions, and can be used for battery thermal management and thermal runaway protection design.

[0081] In this document, the terms "upper", "lower", "front", "back", "left", "right", "top", "bottom", "inner", "outer", "vertical", and "horizontal" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the purpose of clarifying the technical solution and facilitating description, and therefore should not be construed as limiting the present invention.

[0082] In this document, the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, which includes not only the elements listed but also other elements not expressly listed.

[0083] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for determining the radial thermal conductivity and specific heat of a cylindrical battery, characterized in that, Includes the following steps: S1. A number of thermal protection batteries are arranged around the battery under test as the center. The battery under test and the number of thermal protection batteries are connected by an insulating collar bracket (2) structure to form a battery pack (10). A thermocouple (11) of the battery under test is arranged at the upper, middle and lower ends of the side of the battery under test. A thermocouple (11) of the thermal protection battery is arranged on the surface of one of the thermal protection batteries. S2. Thin film heaters (5) are provided on the sides of both the battery under test and the thermal protection battery, and a heat flow meter (8) is provided on the outside of the thin film heater (5) of the battery under test. Then, a high thermal conductivity graphite sheet (4) is provided between the thin film heater (5) and the corresponding battery under test or thermal protection battery. The high thermal conductivity graphite sheet (4) is used to balance the heat flow entering the battery. S3. The top, sides and bottom of the battery pack (10) are covered with heat-insulating felt (1) to form a test section; then the battery pack (10) is placed in the temperature control box (9) and the positive and negative wires of the thin film heater (5) are connected to the DC power supply outside the temperature control box (9) to provide constant heating power. S4. A thermocouple (11) of the temperature control box (9) is installed in the temperature control box (9) to monitor the temperature inside the box, and the thermocouple (11) of the battery under test, the thermocouple (11) of the thermal protection battery and the thermocouple (11) of the temperature control box (9) are connected to the data acquisition instrument (12) to output temperature signal and voltage signal; S5. Keep the temperature of the temperature control box (9) unchanged from the initial temperature. When the battery temperature and the temperature inside the box reach thermal equilibrium, heat the battery under test and the thermal protection battery through the thin film heater (5) and record the change in the side temperature of the battery under test. Stop heating 100-800s after heating to the quasi-steady state. Let the length of the battery under test be H, the radius be r, the base area be A, the density be ρ, and the radial thermal conductivity be k. r The heating power of the thin-film heater (5) is Q, and the average heating heat flux density on the side of the battery is q=Q / (πDH)-q loss , where q loss Let be the average heat flux density lost at the outer surface, and ΔT be the average temperature rise on the side of the battery. Then, the specific heat c of the battery can be expressed by the temperature rise rate dT / dt at the quasi-steady state as: The radial thermal conductivity k r It can be expressed by temperature rise ΔT, battery specific heat c, radius r, heat flux q, and Fourier number Fo: Among them, F O =krt / ρcr 2 .

2. The method for determining the radial thermal conductivity and specific heat of a cylindrical battery according to claim 1, characterized in that, Includes the following steps: X1. Based on steps S1-S5, obtain the battery's temperature rise curve and the average heat flux density q of the external surface loss. loss Thus, we obtain q and the temperature rise ΔT = ΔT1(t); X2. Calculate the battery specific heat c and instantaneous thermal conductivity k using the above formula. r1 and transient variable Fo1=kr1t / (ρcr 2 The curve relationship between kr and kr1(Fo1) is kr = kr1(Fo1), k r1 Covers the range of measured thermal conductivity; X3. The obtained instantaneous thermal conductivity k r1 Divide the time range into 5-10 equal parts, based on each k r1 Based on the specific heat c and the constant heat flux boundary condition q, a single-cell thermal model is established for transient numerical simulation. The thermal conductivity k is input separately. r1 And obtain the temperature rise ΔT = ΔT2 corresponding to the same time period t; X4. For each input thermal conductivity k r1 In the simulation scenario, based on the temperature rise ΔT2 and t from the numerical simulation, the above k... r The corresponding thermal conductivity k can be obtained by formula. r2 (t) and divide it equally, k r2 (t) Equal division of time range and k r1 (t) are the same; X5. Based on the simulated instantaneous thermal conductivity k r2 (t) Calculate the relative Fo2 = kr2t / (ρcr) 2 Plot the thermal conductivity k at the same time t with Fo2(t) as the horizontal axis. r1 With thermal conductivity k r2 (t) The relationship curve between the deviation of the two and Fo2, and the range of Fourier numbers Fo2 corresponding to the determined minimum deviation interval; X6. Substitute k according to the determined Fo2 range. r Formula k r =k r1 (Fo) Back-calculate the corresponding thermal conductivity k r Range, taking k r The average value is the thermal conductivity to be measured.

3. The method for determining the radial thermal conductivity and specific heat of a cylindrical battery according to claim 1, characterized in that, The test battery and the thermal protection battery in step S1 have similar radial thermal conductivity, and all thin film heaters (5) have the same heating power. The structure of the thermal insulation ring bracket (2) is a cylinder with a hollowed-out middle section to accommodate the battery according to the battery arrangement. The gaps between the batteries are filled with thermal insulation felt material.

4. The method for determining the radial thermal conductivity and specific heat of a cylindrical battery according to claim 1, characterized in that, In step S1, the outer insulating film of the battery under test is peeled off to reduce the contact thermal resistance and measurement error caused by the outer insulating film.

5. The method for determining the radial thermal conductivity and specific heat of a cylindrical battery according to claim 1, characterized in that, In step S2, the high thermal conductivity graphite sheet (4) is a thin graphite sheet with a high thermal conductivity, so as to make the battery temperature uniform. The heat flow meter (8) should be set outside the thin film heater (5), and the position of the heat flow meter (8) should be offset from the positions of the thermocouple (11) of the battery under test and the thermocouple (11) of the thermal protection battery.

6. The method for determining the radial thermal conductivity and specific heat of a cylindrical battery according to claim 1, characterized in that, In step S2, the thin film heater (5) and the heat flow meter (8) are fixed with nylon cable ties to reduce the gap between the thin film heater (5) and the heat flow meter (8) and the battery. A layer of thermally conductive silicone grease is uniformly applied between the thin film heater (5) and the heat flow meter (8) to reduce measurement errors caused by contact.

7. The method for determining the radial thermal conductivity and specific heat of a cylindrical battery according to claim 1, characterized in that, The heat-insulating felt (1) in step S3 is silica aerogel.

8. The method for determining the radial thermal conductivity and specific heat of a cylindrical battery according to claim 1, characterized in that, In step S5, the battery under test and the thermal protection battery are connected to the same device via the power cord of the battery under test to ensure consistent battery heating time.

9. The method for determining the radial thermal conductivity and specific heat of a cylindrical battery according to claim 1, characterized in that, In step S5, based on the experimentally measured specific heat and the heating power provided by the DC power supply, numerical simulation is performed on the case where the thermal conductivity value is between 0 and the maximum possible thermal conductivity value, and the optimal data segment of the experiment when the thermal conductivity value is in this range is determined by numerical simulation. The maximum possible thermal conductivity is calculated by summing the series thermal resistances of the battery's electrode materials and casing materials.

10. An apparatus for implementing the method for measuring the radial thermal conductivity and specific heat of a cylindrical battery as described in any one of claims 1-9, characterized in that, It includes a temperature control box (9), a battery pack (10) placed inside the temperature control box (9), a heating component for heating, and a data acquisition and processing unit for measuring the battery pack (10); The battery pack (10) includes several cylindrical batteries (3). Each cylindrical battery (3) includes a battery under test located at the center and several thermal protection batteries arranged around the battery under test. The battery under test and several thermal protection batteries are connected and fixed by a thermal insulation collar bracket (2). Thermal insulation felt (1) is wrapped around the cylindrical battery (3) and the thermal insulation collar bracket (2). The heating assembly includes a thin-film heater (5) disposed on the side of the cylindrical battery (3), a high thermal conductivity graphite sheet (4) disposed between the thin-film heater (5) and the cylindrical battery (3), the high thermal conductivity graphite sheet (4) being used to balance the heat flow entering the battery, a heat flow meter (8) being disposed outside the thin-film heater (5) of the battery under test, and the thin-film heater (5) and the heat flow meter (8) being connected to a DC power supply (14) through the thin-film heater wire (6) and the heat flow meter wire (7), respectively. The data acquisition and processing unit includes several thermocouples (11). One end of the thermocouple (11) is used to detect the temperature and voltage of the upper, middle and lower ends of the side of the battery under test, the side temperature and voltage of one of the several thermal protection batteries, and the temperature and voltage inside the temperature control box (9). The other end of the thermocouple (11) is connected to the data acquisition instrument (12), and the computer (13) is connected to and controls the data acquisition instrument (12).

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