Method and device for testing specific heat capacity of cylindrical battery and storage medium

Abstract

The invention discloses a method and a device for testing the specific heat capacity of a cylindrical battery. The method comprises a test stage and an analysis stage: in the test stage, a cylindrical battery pasted with a heating sheet is placed in cylindrical foam to form an assembly, constant-power heating and natural cooling experiments are sequentially performed in a constant-temperature environment, and the temperature of the surface of the battery, the temperature of the outer wall of the foam and the temperature of the environment are synchronously collected; in the analysis stage, a slope parameter is obtained by setting an initial value of the specific heat capacity and fitting cooling data in a partition mode so as to calculate system thermal conductance, a true value of the specific heat capacity is iteratively solved based on an energy conservation equation, and convergence is optimized through a dichotomy. The device comprises a constant-power heating system, a cylindrical foam heat insulation structure, a distributed temperature sensing system and a data acquisition and processing system. By establishing the temperature-dependent thermal conductivity model and the intelligent iterative algorithm, accurate measurement of the specific heat capacity of the cylindrical battery is achieved, and the problems that equipment is complex, operation is tedious and precision is insufficient in a traditional method are solved.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a method, apparatus, and storage medium for testing the specific heat capacity of a cylindrical battery. Background Technology

[0002] Lithium-ion and sodium-ion batteries, among other rechargeable batteries, are now widely used in electric vehicles and energy storage systems. To ensure the safety and performance of the batteries during operation, thermal management systems are needed to maintain them within a reasonable temperature range and maximize temperature uniformity. The design and operation of thermal management systems rely heavily on precise understanding of the battery's thermal performance.

[0003] The thermal performance of a battery mainly includes thermal conductivity and specific heat capacity: thermal conductivity is an important parameter affecting temperature uniformity, reflecting the battery's ability to conduct heat; specific heat capacity reflects the battery's ability to absorb and release heat per unit time.

[0004] Taking specific heat capacity as an example, the main known methods for testing the specific heat capacity of batteries are:

[0005] 1. Adiabatic Accelerated Calorimeter (ARC) Method: This method relies on an adiabatic accelerated calorimeter (including an adiabatic reaction chamber, temperature sensor, programmed temperature rise module, and data acquisition system). The operation process involves placing the battery sample into the adiabatic reaction chamber and sealing it. The programmed temperature rise module heats the sample while maintaining the adiabatic environment inside the chamber, and the temperature change data is recorded. The specific heat capacity is calculated by combining the sample mass. Although this method has high accuracy, the equipment is expensive and the operation is complex. Furthermore, it is limited by the size of the sample chamber and cannot test large-sized batteries. In addition, this method is currently mainly applicable to prismatic batteries and is rarely used in the field of specific heat capacity testing of cylindrical batteries.

[0006] 2. Differential Scanning Calorimetry (DSC): This method requires a differential scanning calorimeter (including a sample cell, reference cell, heating furnace, temperature difference detector, and inert gas protection system). During the test, a material-grade sample is first extracted from the battery and placed in the sample cell. An inert substance is placed in the reference cell. After inert gas is introduced to eliminate interference, heating is started. The specific heat capacity of the material is calculated by monitoring the heat flow difference between the sample and the reference cell. The limitation of this method is that it is only applicable to material-grade samples and cannot be used to test complete batteries.

[0007] 3. Mixed calorimetry: This method relies on a mixed calorimeter (including an adiabatic mixing container, a constant temperature bath, a stirrer, a temperature sensor, a pipette, and an electronic balance). The specific procedure is as follows: first, a solvent with a known specific heat capacity is weighed using an electronic balance and injected into the mixing container. After the temperature is balanced in the constant temperature bath, the pretreated battery sample is placed in the container and stirring is started. After the system temperature stabilizes, the change data is recorded, and the specific heat capacity of the battery is calculated according to the energy conservation formula. Since the operation requires precise control of multiple links and relies on the coordination of multiple precision instruments, the overall operation is relatively complex.

[0008] 4. Traditional constant power heating method: The main equipment includes a constant power heating source, thermocouple, timer, data logger and electronic balance. In actual operation, the mass of the battery sample is weighed first, then the heating source is placed close to the surface of the battery and the thermocouple is fixed to monitor the temperature. After setting a constant power for heating, the temperature and time are recorded simultaneously. The specific heat capacity is calculated using the energy formula. This method has simple equipment and is easy to operate, but the test accuracy is low because it does not consider the environmental heat loss during heating.

[0009] Therefore, there is a need to develop battery specific heat capacity testing technology that is simple to use, easy to operate, and highly accurate for various types of batteries. Summary of the Invention

[0010] This invention addresses the specific heat capacity testing requirements of cylindrical batteries. Based on the constant power heating method and the principle of heat loss compensation, combined with a radial heat conduction model of a cylinder, it quantifies heat loss through a distributed temperature sensing system and uses an iterative algorithm to accurately calculate the battery's specific heat capacity.

[0011] The present invention adopts the following technical solution:

[0012] In a first aspect, the present invention provides a method for testing the specific heat capacity of a cylindrical battery, the method comprising a testing phase and an analysis phase:

[0013] The testing phase includes:

[0014] A cylindrical battery with a heating element attached is placed in a cylindrical foam to form a battery-foam assembly;

[0015] The assembly was placed in a large, temperature-controlled space, and the battery surface temperature T was measured simultaneously. s Foam outer wall temperature T o and ambient temperature T e ;

[0016] A constant power heating experiment and a natural cooling experiment were conducted successively, and the temperature changes of each measuring point over time were recorded in the two experimental stages.

[0017] The analysis phase includes the following steps:

[0018] S1. Set the battery specific heat capacity estimation value c g ;

[0019] S2. Divide the numerical temperature range of the outer wall of the foam during the cooling stage into multiple intervals;

[0020] For the cooling data within each interval, a linear regression is performed based on the following equation to obtain the slope parameter k(T) for each interval. o ):

[0021] -dT s / dt=k(To )*(T s -T e (1)

[0022] t represents time, k(T) o () indicates that the temperature of the outer wall of the foam is T. o The slope parameter at that time;

[0023] Based on the slope parameter k for each interval, the system thermal conductivity G(T) for each temperature interval is calculated. o ):

[0024] G(T o )=k(T o )*m*c g (2)

[0025] The mass m above represents the mass of the cylindrical battery.

[0026] S3. During the heating phase, the corresponding system thermal conductivity is determined based on the real-time measured temperature of the foam outer wall. The specific heat capacity c of the battery at each moment is then calculated using the following energy conservation equation. c :

[0027] P=m*c c *dT s / dt+G(T o )*(T s -T e (3)

[0028] The calculated specific heat capacity c of the battery at each time point c The average value is used as the calculated value c of the battery specific heat capacity in this step. c The output is given, where P represents the heating power.

[0029] S4, if |c c -c g If the value is less than the preset tolerance, the analysis ends and the calculated battery specific heat capacity value c is output. c The result is the test result; otherwise, proceed to S5.

[0030] S5, Update battery specific heat capacity estimate c g And return to S2.

[0031] Optionally, the cylindrical foam has cylindrical cavities to accommodate the cylindrical battery, wherein the height and diameter of the cylindrical cavity are a times and b times that of the cylindrical battery, respectively, where a is between 1.1 and 2, and b is between 0.90 and 0.99.

[0032] Optionally, the axis and center of the cylindrical foam, the cylindrical cavity, and the cylindrical battery all coincide.

[0033] Optionally, the ratio of the volume of the large space to the volume of the assembly is greater than 10,000.

[0034] Optionally, the start time of the natural cooling experiment is the end time of the constant power heating experiment, and the end time of the natural cooling experiment is when the difference between the battery surface temperature and the ambient temperature is less than a preset value or the total natural cooling time reaches a preset value.

[0035] Optionally, the power value of the constant power heating stage is set to make the battery surface temperature rise rate between 0.2 and 2°C / minute.

[0036] Optionally, during the constant power heating stage, the maximum temperature rise on the battery surface is between 10 and 20°C.

[0037] Optionally, the setting and updating of the battery specific heat capacity guess value in steps S1 and S5 is implemented using a binary search method, specifically including:

[0038] Preset lower limit c of the battery specific heat capacity prediction value a and the initial upper limit c b ;

[0039] In step S1, the estimated value of the battery specific heat capacity c is set. g =(c a +c b ) / 2;

[0040] In step S5:

[0041] 1) If c c >c g Let c a =c g ;

[0042] 2) If c c <c g Let c b =c g ;

[0043] Then update c g =(c a +c b ) / 2.

[0044] According to a second aspect of the present invention, an apparatus is provided for a method of testing the specific heat capacity of a cylindrical battery as described above, comprising:

[0045] A constant power heating system, including heating elements attached to the surface of the battery, for providing controllable constant heating power;

[0046] The heat-insulating support structure is a hollow column made of cylindrical foam, the hollow part of which is used to accommodate the cylindrical battery;

[0047] A temperature sensing system, including temperature sensors arranged on the battery surface, the foam outer wall, and the environment, for simultaneously measuring the battery surface temperature, the foam outer wall temperature, and the ambient temperature;

[0048] A data acquisition system is used to collect and store temperature data;

[0049] The data processing system is used to execute each step of the analysis phase and calculate the specific heat capacity of the battery.

[0050] According to a third aspect of the present invention, a computer-readable storage medium is provided, storing a plurality of computer instructions adapted for loading by a processor to execute the above-described method for testing the specific heat capacity of a cylindrical battery.

[0051] The beneficial effects of this invention will be described below in conjunction with the principles of its technical solution.

[0052] The core of this invention is a unified heat loss model based on the total thermal conductivity of the system, which simplifies the experimental setup and data processing flow while ensuring measurement accuracy. The total thermal conductivity model is a temperature-dependent dynamic model. By fitting the cooling stage data piecewise according to the temperature of the outer wall of the foam, the changes in convective heat transfer are accurately captured, thereby enabling more accurate heat loss compensation during the heating stage.

[0053] This invention simplifies the battery by using lumped parameters, assuming that the heat capacity of the battery under various states is concentrated at a single point mass, the temperature of which can change over time. The cylindrical cavity accommodating the cylindrical battery is set with a height and b times the size of the cylindrical battery, where a is between 1.1 and 2, and b is between 0.90 and 0.99. This serves two purposes: firstly, it creates an interference fit radially, ensuring a tight fit between the outer wall of the cylindrical battery and the inner wall of the cylindrical foam, minimizing contact thermal resistance; secondly, it creates a clearance fit axially, forming an air gap between the two end faces of the cylindrical battery and the two end faces of the cylindrical cavity. Since air has very low thermal conductivity, this significantly increases the axial thermal resistance of the cylindrical battery, causing heat loss primarily to occur radially. This simplifies the heat transfer in the experimental setup to a one-dimensional radial heat transfer problem.

[0054] Considering that the thermal response rate of the foam is typically much faster than the rate of change in battery temperature, the heat conduction through the foam layer can be considered steady-state within any small time interval dt. During the experiment, the heat transfer process of the device is as follows: heat from the battery with the heating element attached is transferred to the inner wall of the foam via conduction; the inner wall then transfers heat to the outer wall via conduction; and finally, the outer wall transfers heat to the surrounding atmosphere via convection. The total thermal conductance involved includes the series connection of three parts: the contact thermal conductance between the battery and the inner wall of the foam, the foam thermal conductance, and the convective thermal conductance between the outer wall of the foam and the environment. Although the ambient temperature can be kept relatively constant during the experiment, the temperature of the outer wall of the foam varies. An increased temperature difference between the two can drive stronger airflow and enhance heat transfer; therefore, the convective thermal conductance between the outer wall of the foam and the environment is related to the temperature of the outer wall of the foam, while the contact thermal conductance between the battery and the inner wall of the foam and the foam thermal conductance remain constant during the experiment.

[0055] During the natural cooling stage, the heat balance equation is:

[0056] -m*c*dT s =G*(T s -T e )*dt

[0057] In the formula, m and c are the mass and specific heat capacity of the battery, respectively; G is the total thermal conductivity of the experimental setup during the heat transfer process, in W / ℃; T s T e These represent the battery surface temperature and the ambient temperature, respectively; dt is the time element, dT s dT represents the change in battery surface temperature within a time infinitesimal element. Since the battery surface temperature maintains a decreasing trend during the natural cooling phase, dT... s Since the result is negative, a negative sign is added to the left side of the equation.

[0058] Let k = G / mc, then we can simplify to get the following formula:

[0059] -dT s / dt=k(T o )*(T s -T e (1)

[0060] In equation (1), k(T) o () indicates the temperature T of the outer wall of the foam. o The cooling data within each interval is linearly regressed based on the equation in equation (1) to obtain the slope parameter k(T) corresponding to each interval. o That is, with -dT s / dt is the ordinate, (T) s -T e Plotting a line with the x-axis as the abscissa, and fitting the line using the least squares method according to the equation in equation (1), the slope of the line is obtained, which is the slope parameter k(T).o ).

[0061] In practical applications, since the battery's mass m is easily measured in advance while its specific heat capacity c is unknown, a guessed value c is used. g Instead of its true value, that is, based on the slope parameter k(T) for each interval. o Further calculations were performed on the system thermal conductivity G(T) for each temperature range. o ):

[0062] G(T o )=k(T o )*m*c g (2)

[0063] During the heating phase, the temperature T of the outer wall of the foam is measured in real time. o Determine the corresponding system thermal conductivity G(T) o The specific heat capacity c of the battery at each moment is calculated using the following energy conservation equation. c :

[0064] P=m*c c *dT s / dt+G(T o )*(T s -T e (3)

[0065] The calculated specific heat capacity c of the battery at each time point c The average value is used as the calculated value c of the battery specific heat capacity in this step. c The output is given, where P represents the heating power.

[0066] That is, the calculated value of the battery specific heat capacity c at each time point. c =dt*[PG(T o )*(T s -T e )] / (m*dT s The calculated specific heat capacity c of the battery obtained at each moment during the heating phase is used. c Then calculate the average as its output.

[0067] If the calculated value matches the previously set guess value c g If the deviation is less than the preset threshold, the guess is considered correct, and the calculated value is used as the true value to output the final result. Otherwise, the guess value is updated and the calculation is repeated until the guess is correct. When the calculation is considered to have converged, the analysis and calculation can be completed.

[0068] Furthermore, to improve convergence efficiency, a "binary search method" can be used during the update of the guessed value, namely:

[0069] Preset lower limit c of the battery specific heat capacity prediction valuea and the initial upper limit c b That is, the battery specific heat capacity prediction value is set as the arithmetic average of the preset initial lower limit and the initial upper limit of the battery specific heat capacity prediction value.

[0070] In step S1, the estimated value of the battery specific heat capacity c is set. g =(c a +c b ) / 2;

[0071] In step S5:

[0072] 1) If c c >c g Let c a =c g ;

[0073] 2) If c c <c g Let c b =c g ;

[0074] Then update c g =(c a +c b ) / 2.

[0075] That is, in step S5, if the current calculated value of the battery specific heat capacity is greater than the current guessed value of the battery specific heat capacity, the lower limit of the guessed value of the battery specific heat capacity is updated to the current guessed value of the battery specific heat capacity; if the current calculated value of the battery specific heat capacity is less than the current guessed value of the battery specific heat capacity, the upper limit of the guessed value of the battery specific heat capacity is updated to the current guessed value of the battery specific heat capacity; finally, the guessed value of the battery specific heat capacity is set as the arithmetic mean of the lower limit and the upper limit of the current guessed value of the battery specific heat capacity, and then the next round of solving and comparing the battery specific heat capacity is started.

[0076] This invention provides a technical solution for testing the specific heat capacity of cylindrical batteries, which differs from currently known technologies. Its beneficial effects include the following four aspects:

[0077] 1. Although the axial thermal conductivity of a cylindrical battery is usually much higher than its radial thermal conductivity, this invention sets an air gap between the two ends of the cylindrical battery and the cylindrical foam. By utilizing the low thermal conductivity of still air, the heat loss at the ends is suppressed, and the heat at the battery is guided to dissipate slowly in the radial direction. This makes the heat transfer model conform to the one-dimensional radial steady-state heat transfer characteristics as much as possible, thereby ensuring that the simplified model conforms to the actual situation.

[0078] 2. Based on the known technology of constant power heating for measuring specific heat capacity, this invention fully considers the factor of heat loss to the surrounding environment through foam material, thus greatly improving the measurement accuracy and reliability.

[0079] 3. This invention takes into account the influence of the temperature of the outer wall of the foam on the heat transfer intensity under natural convection conditions in the experimental device. It calculates the total thermal conductivity of the device based on the temperature range of the outer wall of the foam, which helps to improve the accuracy of analysis and testing.

[0080] 4. This invention proposes to use a "guess-verify" method to obtain the specific heat capacity of a cylindrical battery, and uses a binary search method to update the guess value, which has the advantages of stable and rapid convergence. Attached Figure Description

[0081] Figure 1 This is a cross-sectional view of the battery-foam assembly in an embodiment of the present invention. In the figure, 1 is a cylindrical battery, 2 is a heating element, and 3 is a cylindrical foam.

[0082] Figure 2 This is a flowchart of the analysis phase in the method for testing the specific heat capacity of a cylindrical battery in an embodiment of the present invention.

[0083] Figure 3 This is a flowchart illustrating the method for testing the specific heat capacity of a cylindrical battery in this embodiment of the invention, which uses a binary search method to set and update the estimated value of the battery's specific heat capacity.

[0084] Figure 4 This is a temperature change curve over time during the heating stage in an embodiment of the present invention.

[0085] Figure 5 This is a temperature change curve over time during the natural cooling stage in an embodiment of the present invention.

[0086] Figure 6 In this embodiment of the invention, the first temperature range during the natural cooling stage is -dT s / dt and (T s -T e A fitting plot of the relationship.

[0087] Figure 7 In this embodiment of the invention, the second temperature range during the natural cooling stage is -dT s / dt and (T s -T e A fitting plot of the relationship. Detailed Implementation

[0088] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0089] like Figure 2 As shown, this invention provides a method for testing the specific heat capacity of a cylindrical battery, including a testing phase and an analysis phase:

[0090] The testing phase includes:

[0091] A cylindrical battery with a heating element attached is placed inside a cylindrical foam to form a battery-foam assembly. A cross-sectional view of this assembly is shown below. Figure 1 For ease of observation, Figure 1 The dimensions and proportions in the drawing are not based on the actual situation;

[0092] The assembly was placed in a large, temperature-controlled space, and the battery surface temperature T was measured simultaneously. s Foam outer wall temperature T o and ambient temperature T e ;

[0093] A constant power heating experiment and a natural cooling experiment were conducted successively. Data on the temperature changes over time at each measuring point were recorded during both experimental phases. Figure 4 and Figure 5 As shown;

[0094] The analysis phase includes the following steps:

[0095] S1. Set the battery specific heat capacity estimation value c g ;

[0096] S2. Divide the numerical temperature range of the outer wall of the foam during the cooling stage into multiple intervals;

[0097] See Figure 6 For the cooling data within each interval, a linear regression is performed based on the following equation to obtain the slope parameter k(T) for each interval. o ):

[0098] -dT s / dt=k(T o )*(T s -T e (1)

[0099] t represents time, k(T) o () indicates that the temperature of the outer wall of the foam is T. o The slope parameter at that time;

[0100] Based on the slope parameter k for each interval, the system thermal conductivity G(T) for each temperature interval is calculated. o ):

[0101] G(T o )=k(T o )*m*c g (2)

[0102] The mass m above represents the mass of the cylindrical battery.

[0103] S3. During the heating phase, the corresponding system thermal conductivity is determined based on the real-time measured temperature of the foam outer wall. The specific heat capacity c of the battery at each moment is then calculated using the following energy conservation equation. c :

[0104] P=m*c c *dT s / dt+G(T o )*(T s -T e (3)

[0105] The calculated specific heat capacity c of the battery at each time point c The average value is used as the calculated value c of the battery specific heat capacity in this step. c The output is given, where P represents the heating power.

[0106] S4, if |c c -c g If the value is less than the preset tolerance, the analysis ends and the calculated battery specific heat capacity value c is output. c The result is the test result; otherwise, proceed to S5.

[0107] S5, Update battery specific heat capacity estimate c g And return to S2.

[0108] Preferably, the cylindrical foam has cylindrical cavities to accommodate the cylindrical battery, and the height and diameter of the cylindrical cavity are a times and b times that of the cylindrical battery, respectively, where a is between 1.1 and 2 and b is between 0.90 and 0.99.

[0109] Preferably, the axis and center of the cylindrical foam, the cylindrical cavity, and the cylindrical battery all coincide.

[0110] Preferably, the ratio of the volume of the large space to the volume of the assembly is greater than 10,000, thereby ensuring a constant temperature and stability of the external atmospheric environment.

[0111] Preferably, the start time of the natural cooling experiment is the end time of the constant power heating experiment, and the end time of the natural cooling experiment is when the difference between the battery surface temperature and the ambient temperature is less than a preset value or the total natural cooling time reaches a preset value. Preferably, the preset value for the difference between the battery surface temperature and the ambient temperature can be between 0.5℃ and 2.0℃; the preset value for the total natural cooling time can be between 20 minutes and 120 minutes.

[0112] Preferably, the power value of the constant power heating stage is set to make the battery surface temperature rise rate between 0.2 and 2°C / minute.

[0113] Preferably, during the constant power heating stage, the maximum temperature rise on the battery surface is between 10 and 20°C.

[0114] Preferably, such as Figure 3 As shown, the setting and updating of the battery specific heat capacity guess value in steps S1 and S5 is implemented using a binary search method, specifically including:

[0115] Preset lower limit c of the battery specific heat capacity prediction value a and the initial upper limit c b ;

[0116] In step S1, the estimated value of the battery specific heat capacity c is set. g =(c a +c b ) / 2;

[0117] In step S5:

[0118] 1) If c c >c g Let c a =c g ;

[0119] 2) If c c <c g Let c b =c g ;

[0120] Then update c g =(c a +c b ) / 2.

[0121] This invention provides an apparatus for testing the specific heat capacity of the above-mentioned cylindrical battery, comprising:

[0122] A constant power heating system, including heating elements attached to the surface of the battery, for providing controllable constant heating power;

[0123] The heat-insulating support structure is a hollow column made of cylindrical foam, the hollow part of which is used to accommodate the cylindrical battery;

[0124] The temperature sensing system includes temperature sensors arranged on the battery surface, the foam outer wall, and the environment to simultaneously measure the battery surface temperature, the foam outer wall temperature, and the ambient temperature. Specifically, one or more temperature sensors can be set in each of the three areas. If multiple temperature sensors are set in the same area, the average value of their measurements is used as the temperature measurement result output.

[0125] A data acquisition system is used to collect and store temperature data;

[0126] The data processing system is used to execute each step of the analysis phase and calculate the specific heat capacity of the battery.

[0127] The present invention also provides a computer-readable storage medium storing a plurality of computer instructions, the computer instructions being adapted for loading by a processor to execute the above-described method for testing the specific heat capacity of a cylindrical battery.

[0128] Example

[0129] like Figure 1 As shown, the object under test in this example is an 18650 lithium iron phosphate cylindrical battery with a mass of m=45g, a diameter of 18mm and a height of 65mm; the cylindrical foam has a diameter of 40mm and a height of 90mm, and has a cylindrical cavity with a diameter of 17.8mm and a height of 75mm to accommodate the cylindrical battery. The distance between the end face of the cylindrical battery and the end face of the cylindrical cavity is 5mm.

[0130] A cylindrical battery with a polyimide heating element attached is placed in a cylindrical foam to form a battery-foam assembly. The heating element is electrically connected to a regulated DC power supply through a thin wire passing through the assembly, and the heating power value can be adjusted.

[0131] The assembly was placed in a large room at a temperature of 20 ± 0.2℃, and the battery surface temperature T was measured synchronously at 30-second intervals. s Foam outer wall temperature T o and ambient temperature T e .

[0132] After the assembly was allowed to stand for 24 hours to reach the same temperature as the ambient temperature, a constant power heating experiment was started. The heating power was P=1.5W, and the heating time was 10 minutes. The temperature change curves of various parts during the heating stage are shown in the figure. Figure 4 .

[0133] After heating, the natural cooling phase began, and the experiment ended after a total natural cooling time of 35 minutes. The temperature change curves at various points during the natural cooling phase are shown in the figure. Figure 5 .

[0134] To facilitate analysis, the collected temperature curves in this embodiment have been smoothed and noise-reduced.

[0135] according to Figure 2 The flowchart shown is analyzed; specifically, it employs... Figure 3 The binary method shown enables the setting and updating of the battery specific heat capacity prediction value.

[0136] In this embodiment, the numerical temperature range of the outer wall of the foam during the cooling stage is divided into two intervals: ≥21.5℃ and <21.5℃, which are respectively denoted as the first temperature curve and the second temperature interval.

[0137] The first temperature range during the natural cooling stage, namely the temperature T of the foam outer wall... o -dT within the range of ≥21.5℃ s / dt and (Ts -T e The fitting plot of the relationship is shown in the figure. Figure 6 The second temperature range during the natural cooling stage, namely the temperature T of the outer wall of the foam. o -dT in the range of <21.5℃ s / dt and (T s -T e The fitting plot of the relationship is shown in the figure. Figure 7 .

[0138] Figure 6 and Figure 7 goodness of fit R 2 All values ​​are greater than 0.999, indicating a very good fit, and the entire process basically conforms to the model assumptions. Figure 6 and Figure 7 From the fitting equation, we can see that k(T) o (≥21.5℃) = 0.00024s -1 ,k(T o <21.5℃) = 0.00023s -1 .

[0139] The following describes the analysis phase.

[0140] Preset lower limit c of the battery specific heat capacity prediction value a =1500J / (kg·℃) and initial upper limit c b =2000J / (kg·℃).

[0141] In step S1, the estimated value of the battery specific heat capacity c is set. g =(c a +c b ) / 2=(1500+2000) / 2=1750J / (kg·℃).

[0142] In step S2, the numerical temperature range of the foam outer wall during the cooling stage is divided into two intervals: ≥21.5℃ and <21.5℃.

[0143] For the cooling data within each interval, the slope parameter k(T) for each interval is obtained through linear regression. o ) is: k(T o (≥21.5℃) = 0.00024s -1 ,k(T o <21.5℃) = 0.00023s -1 .

[0144] Further calculations were performed on the system thermal conductivity G(T) for each temperature range. o )for:

[0145] G(T o ≥21.5℃)=k(To ≥21.5℃)*m*c g =0.00024*0.045*1750=0.0189W / ℃;

[0146] G(T o <21.5℃)=k(T o <21.5℃)*m*c g =0.00023*0.045*1750=0.0181W / ℃.

[0147] In step S3, during the heating stage, the corresponding system thermal conductivity is determined based on the real-time measured temperature of the foam outer wall. The specific heat capacity c of the battery at each moment is then calculated using the following energy conservation equation. c :

[0148] P=m*c c *dT s / dt+G(T o )*(T s -T e (3)

[0149] The calculated specific heat capacity c of the battery at each time point c The average value is used as the calculated value c of the battery specific heat capacity in this step. c The output is given, where P represents the heating power.

[0150] That is, the calculated value of the battery specific heat capacity c at each time point. c =dt*[PG(T o )*(T s -T e )] / (m*dT s The calculated specific heat capacity c of the battery obtained at each moment during the heating stage is used. c The average is then calculated as the output. The calculation data is shown in Table 1.

[0151] The calculation begins after the data from the second time point collected during the heating process, taking t=30s as an example to illustrate the calculation process.

[0152] Since at t=30s, T o =20.01℃<21.5℃, therefore:

[0153] G(T o )= G(T o <21.5℃) = 0.0181W / ℃,

[0154] c c =dt*[PG(T o )*(T s -T e )] / (m*dTs = 30*[1.5-0.0181*(20.58-20.03)] / [0.045*(20.58-20.03)]=1806J / (kg·℃). Please note that dT in this calculation... s T is the value of T at t=30s s The value of T at t=0s s The difference in value.

[0155] The calculated specific heat capacity c of the battery at each time point in Table 1 c The arithmetic mean is 1738 J / (kg·℃), which is used as the calculated value c for the battery's specific heat capacity in this step. c The output of .

[0156] Table 1. Calculated specific heat capacity c of the battery at various times during the heating phase. c

[0157] Time / s <![CDATA[T s / ℃]]> <![CDATA[T o / ℃]]> <![CDATA[T e / ℃]]> <![CDATA[G(T o ) / (W / ℃)]]> <![CDATA[c c / (J / (kg·℃))]]> 0 20.03 20.01 19.96 0.0181 30 20.58 20.10 20.03 0.0181 1806 60 21.15 20.20 20.00 0.0181 1730 90 21.72 20.31 20.01 0.0181 1718 120 22.28 20.41 19.99 0.0181 1737 150 22.84 20.51 19.98 0.0181 1724 180 23.39 20.61 19.99 0.0181 1744 210 23.94 20.70 20.04 0.0181 1733 240 24.49 20.80 20.00 0.0181 1720 270 25.03 20.89 20.03 0.0181 1741 300 25.57 20.97 20.01 0.0181 1728 330 26.10 21.05 20.04 0.0181 1750 360 26.63 21.13 19.97 0.0181 1736 390 27.16 21.20 20.05 0.0181 1726 420 27.68 21.27 19.98 0.0181 1745 450 28.20 21.33 20.03 0.0181 1735 480 28.71 21.40 19.99 0.0181 1756 510 29.22 21.46 19.98 0.0181 1743 540 29.73 21.52 20.02 0.0189 1722 570 30.24 21.57 19.98 0.0189 1709 600 30.73 21.63 19.95 0.0189 1765

[0158] In this embodiment, convergence is considered complete when the absolute value of the difference between the calculated and guessed specific heat capacity of the battery is less than 5 J / (kg·℃). In step 4, because |c c -c g The value is |=|1738-1750|=12J / (kg·℃), which is greater than the preset tolerance of 5J / (kg·℃), so proceed to step 5.

[0159] In step S5, the estimated specific heat capacity value c of the battery needs to be updated. g And return to step S2. Therefore, c c =1738J / (kg·℃), c g =1750J / (kg·℃), therefore c c <c g Let c b =c g =1750J / (kg·℃), update c g =(c a +c b ) / 2=(1500+1750)=1625 J / (kg·℃) and return to step S2.

[0160] As shown in Table 2, after several iterations, the final |c c -c g If the value is less than the preset tolerance, the convergence condition is met, the analysis process ends, and the calculated battery specific heat capacity c is output. c =1738 J / (kg·℃) is the test result.

[0161] Table 2 Summary of Iteration Process

[0162] Number of iterations / times <![CDATA[c a / (J / (kg·℃))]]> <![CDATA[c b / (J / (kg·℃))]]> <![CDATA[c g / (J / (kg·℃))]]> <![CDATA[c c / (J / (kg·℃))]]> <![CDATA[|c c -c g | / (J / (kg·℃))]]> 1 1500 1750 1625 1738 113 2 1625 1750 1687 1748 61 3 1687 1750 1718 1742 24 4 1718 1750 1734 1740 6 5 1734 1750 1742 1739 3

[0163] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for testing the specific heat capacity of a cylindrical battery, characterized in that, Includes testing and analysis phases: The testing phase includes: A cylindrical battery with a heating element attached is placed in a cylindrical foam to form a battery-foam assembly; The assembly was placed in a large, temperature-controlled space, and the battery surface temperature T was measured simultaneously. s Foam outer wall temperature T o and ambient temperature T e ; A constant power heating experiment and a natural cooling experiment were conducted successively, and the temperature changes of each measuring point over time were recorded in the two experimental stages. The analysis phase includes the following steps: S1. Set the battery specific heat capacity estimation value c g ; S2. Divide the numerical temperature range of the outer wall of the foam during the cooling stage into multiple intervals; For the cooling data within each interval, a linear regression is performed based on the following equation to obtain the slope parameter k(T) for each interval. o ): -dT s / dt=k(T o )*(T s -T e ) (1) t represents time, k(T) o () indicates that the temperature of the outer wall of the foam is T. o The slope parameter at that time; Based on the slope parameter k for each interval, the system thermal conductivity G(T) for each temperature interval is calculated. o ): G(T o )=k(T o )*m*c g (2) The mass m above represents the mass of the cylindrical battery. S3. During the heating phase, the corresponding system thermal conductivity is determined based on the real-time measured temperature of the foam outer wall. The specific heat capacity c of the battery at each moment is then calculated using the following energy conservation equation. c : P=m*c c *dT s / dt+G(T o )*(T s -T e ) (3) The calculated specific heat capacity c of the battery at each time point c The average value is used as the calculated value c of the battery specific heat capacity in this step. c The output is given, where P represents the heating power. S4, if |c c -c g If the value is less than the preset tolerance, the analysis ends and the calculated battery specific heat capacity value c is output. c The result is the test result; otherwise, proceed to S5. S5, Update battery specific heat capacity prediction value c g And return to S2.

2. The method for testing the specific heat capacity of a cylindrical battery according to claim 1, characterized in that, The cylindrical foam has cylindrical cavities to accommodate the cylindrical battery. The height and diameter of the cylindrical cavity are a times and b times that of the cylindrical battery, respectively, where a is between 1.1 and 2, and b is between 0.90 and 0.

99.

3. The method for testing the specific heat capacity of a cylindrical battery according to claim 1 or 2, characterized in that, The axis and center of the cylindrical foam, the cylindrical cavity, and the cylindrical battery all coincide.

4. The method for testing the specific heat capacity of a cylindrical battery according to claim 1, characterized in that, The ratio of the volume of the large space to the volume of the assembly is greater than 10000.

5. The method for testing the specific heat capacity of a cylindrical battery according to claim 1, characterized in that, The start time of the natural cooling experiment is the end time of the constant power heating experiment, and the end time of the natural cooling experiment is when the difference between the battery surface temperature and the ambient temperature is less than a preset value or the total natural cooling time reaches a preset value.

6. The method for testing the specific heat capacity of a cylindrical battery according to claim 1, characterized in that, The power value of the constant power heating stage is set to keep the battery surface temperature rise rate between 0.2 and 2°C / minute.

7. The method for testing the specific heat capacity of a cylindrical battery according to claim 1, characterized in that, During the constant power heating stage, the maximum temperature rise on the battery surface is between 10 and 20°C.

8. The method for testing the specific heat capacity of a cylindrical battery according to claim 1, characterized in that, The setting and updating of the battery specific heat capacity guess value in steps S1 and S5 are implemented using a binary search method, specifically including: Preset lower limit c of the battery specific heat capacity prediction value a and the initial upper limit c b ; In step S1, the estimated value of the battery specific heat capacity c is set. g =(c a +c b ) / 2; In step S5: 1) If c c >c g Let c a =c g ; 2) If c c <c g Let c b =c g ; Then update c g =(c a +c b ) / 2.

9. An apparatus for testing the specific heat capacity of a cylindrical battery according to any one of claims 1-8, characterized in that, include: A constant power heating system, including heating elements attached to the surface of the battery, for providing controllable constant heating power; The heat-insulating support structure is a hollow column made of cylindrical foam, the hollow part of which is used to accommodate the cylindrical battery; A temperature sensing system, including temperature sensors arranged on the battery surface, the foam outer wall, and the environment, for simultaneously measuring the battery surface temperature, the foam outer wall temperature, and the ambient temperature; A data acquisition system is used to collect and store temperature data; The data processing system is used to execute each step of the analysis phase and calculate the specific heat capacity of the battery.

10. A computer-readable storage medium storing a plurality of computer instructions, characterized in that, The computer instructions are adapted to be loaded by the processor to execute the method for testing the specific heat capacity of a cylindrical battery according to any one of claims 1-8.

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