A differential power compensation type battery isothermal calorimeter and dynamic characteristic correction method

Abstract

The present invention discloses a differential power compensation type battery isothermal calorimeter and a dynamic characteristic correction method. The present invention provides a stable temperature boundary by means of a constant temperature heat sink, installs a battery under test and a reference battery of the same model and the same size in a constant temperature calorimeter cavity, and uses a flexible heating sheet to heat to a target temperature. During the charge and discharge process of the battery under test, the power of the reference side heating sheet is used as the baseline power, the output power of the sample side heating sheet is feedback-controlled, and the real-time output powers of the reference side and the sample side heating sheets are collected and recorded. Based on the piecewise fitting of the curve polynomial, a limiting condition is added to the fitting curve, and the limiting condition is that the curve after fitting is continuous at a specified point, so as to obtain the fitted power value and the power change rate value. The real-time heat generation power during the charge and discharge process of the battery under test can be obtained from the difference between the two powers, and thus the heat generation amount of the battery can be calculated by integration. The present invention can reduce the interference caused by the ambient temperature fluctuation and obtain the baseline power that changes in real time.

Description

Technical Field

[0001] The present invention belongs to the field of lithium battery thermal characteristic detection, and particularly relates to a differential power compensation type battery isothermal calorimeter and a dynamic characteristic correction method. Background Art

[0002] At present, the calorimeters applied to the heat generation research of lithium-ion batteries mainly include adiabatic accelerating calorimeters and isothermal calorimeters. The measurement principle of the adiabatic accelerating calorimeter is to keep the temperature of the calorimeter cavity and the object under test dynamically equal, so that the object under test is in an adiabatic state. When the object under test generates heat, the heat is only used to heat the object under test itself, so as to obtain the adiabatic temperature rise. Finally, the heat generation power of the object under test is obtained by calculating the adiabatic temperature rise rate. The measurement principle of the isothermal calorimeter is to keep the temperature of the calorimeter cavity and the object under test constant, so that the object under test is in an isothermal state. When the object under test generates heat, the heating power is adjusted in real time through feedback, so that the temperature of the object under test is maintained constant, so as to obtain the heat generation power of the object under test and measure the heat absorption and release amount under this temperature condition.

[0003] The adiabatic accelerating calorimeter can simulate the thermal characteristics of the heat release reaction process of the battery when the heat inside the battery cannot be dissipated in time, and has rich and diverse functions. It is widely used in the field of battery thermal management. However, it has the following disadvantages: First, the adiabatic accelerating calorimeter has no refrigeration function and cannot quickly track the temperature during the cooling process of the battery, so it is difficult to measure the endothermic effect. Second, due to the existence of the thermal lag effect, the instrument cannot enter a truly adiabatic state, resulting in measurement errors. Third, it is impossible to accurately measure the heat generation power of the battery at a certain fixed temperature point. Compared with the adiabatic accelerating calorimeter, the isothermal calorimeter has the following advantages: First, it can directly measure the heat absorption and release power of the battery. Second, the measurement accuracy of the heat generation power during battery charging and discharging is relatively high. Third, it can accurately measure the charging and discharging heat generation characteristics of the battery at a certain fixed temperature point.

[0004] The basic principles of isothermal calorimeters are divided into the heat flow method and the power compensation method. The specific working principle of the isothermal calorimeter based on the power compensation method is as follows: The external refrigerant circulation provides a constant temperature boundary for the calorimetry system, and the test battery is heated to the target temperature by a heater. After the temperature stabilizes, the output power of the heater is recorded and used as the baseline power. When the battery starts to work, the heat absorption and release effect of the battery causes the temperature of the sensor to change. The temperature control system controls the heater power through feedback to keep the sensor temperature at the target temperature. The change in the heater power is equivalent to the heat effect of the battery. Integrating the heater output power yields the heat generated during the charge and discharge process of the battery. From the working principle, it can be seen that since the heater power is used to feedback-control the battery temperature in real time, the baseline power of the isothermal calorimeter is easily disturbed by ambient temperature fluctuations, and the baseline power data during the calorimetry process cannot be directly obtained. It needs to be obtained by linearly fitting the heater output power and time before and after charge and discharge, resulting in excessive baseline power noise. For common battery isothermal calorimeters based on the power compensation method, the baseline power noise is greater than 10 mW. When the battery capacity is small or the charge and discharge rate is low, the heat generation power of the battery is small. As a result, when the isothermal calorimeter measures the heat generation during the charge and discharge of such batteries, the measurement results have a large error due to noise interference, thus reducing the reference value of the experimental data.

[0005] A method for measuring the heat generation during the charge and discharge of lithium batteries based on the isothermal differential calorimetry method calculates the real-time heat flow during battery operation by measuring the temperature difference between the test battery and the reference battery in the double chamber. Although it can improve the above problems to a certain extent, it is necessary to obtain the system equivalent heat capacity C and equivalent thermal resistance R, and the experimental steps are relatively complex.

[0006] In addition, there is inevitably a certain thermal lag effect in the measurement of heat generation power. On the one hand, the heat generation of lithium batteries mainly comes from the winding core. There is an obvious thermal resistance on the heat transfer path from the winding core to the battery surface, and the heat capacity of the battery itself is relatively large. On the other hand, in order to reduce the contact thermal resistance between the battery and the constant temperature heat sink and improve the temperature uniformity, multiple layers of thermal conductive media, including graphite gaskets, silica gel pads, and heat equalizing blocks, need to be installed on both sides of the battery before testing. The thermal resistance between components cannot be ignored. It can be considered that the measurement of the battery heat generation power involves a non-steady heat transfer process with a delay link. The time lag phenomenon in this process causes the measurement result to not be directly equivalent to the transient heat generation power of the battery.

[0007] Data fitting, as an important method for processing errors and correcting curves, is widely applied in the dynamic characteristic correction of battery isothermal calorimeters. With the increasing complexity of data processing, polynomial fitting has unique advantages in the field of data fitting due to its convenient calculation method and small error. Currently, ordinary polynomial fitting uses a polynomial expansion to fit all the observation points in a small analysis area containing several analysis grid points. Among them, the linear least squares method is a common method for solving curve fitting problems. By using a set of simple and appropriate linearly independent basis functions to approximate experimental data, a fitting function with the smallest overall empirical error can be effectively obtained. , but the regional polynomial fitting of this method is not stable. When there are many data points, if the polynomial order is too low, the fitting accuracy and effect are not ideal. To improve the fitting accuracy and effect, the curve order needs to be increased, but too high an order will bring computational complexity and other disadvantages. Therefore, it is difficult to achieve good fitting accuracy and effect if only one polynomial curve function is used to fit a large number of data points. Summary of the Invention

[0008] Aiming at the disadvantages of large baseline power noise and deficiencies in dynamic characteristics of the battery isothermal calorimeter mentioned in the background technology, the present invention designs a differential power compensation type battery isothermal calorimeter and proposes a method for correcting the dynamic characteristics of the battery isothermal calorimeter based on piecewise polynomial fitting. The present invention can reduce the interference caused by ambient temperature fluctuations, obtain the baseline power that changes in real time, add the constraint condition of continuity at the interval segmentation points for piecewise polynomial fitting, realize the correction of the dynamic characteristics of the battery isothermal calorimeter, thereby improving the accuracy of measuring the heat generation during the charge and discharge of lithium batteries, and the operation is more convenient; when the temperature is above room temperature, an oil bath device is not required, which can reduce costs.

[0009] The present invention provides a differential power compensation type battery isothermal calorimeter, including:

[0010] A sample side device for installing the battery to be tested, the sample side device includes a sample side heat sink, a sample side heat equalizing block, a sample side flexible heating sheet, a sample side thermal conductive silica gel pad, and a sample side temperature sensor; the sample side flexible heating sheet, the sample side heat equalizing block, and the sample side thermal conductive silica gel pad are sequentially stacked on the sample side heat sink, the battery to be tested is installed between the sample side flexible heating sheets, and the sample side temperature sensor is installed in the groove of the sample side heat equalizing block close to the battery side;

[0011] The reference side device is used to install a reference battery. The reference side device includes a reference side heat sink, a reference side heat spreading block, a reference side flexible heating sheet, a reference side thermal conductive silicone pad, and a reference side temperature sensor. The reference side flexible heating sheet, the reference side heat spreading block, and the reference side thermal conductive silicone pad are stacked on the reference side heat sink in sequence. The reference battery is installed between the reference side flexible heating sheets. The reference side temperature sensor is installed in a groove on the side of the reference side heat spreading block close to the battery.

[0012] The calorimetric chamber is used to accommodate the sample side device and the reference side device.

[0013] The temperature control system is used to control the temperature in the calorimetric chamber so that the temperatures of the sample side heat spreading block and the reference side heat spreading block are maintained at the target temperature.

[0014] The data acquisition and processing system is used to collect the output power data of the sample side flexible heating sheet and the reference side flexible heating sheet, and calculate the real-time heat generation power and heat generation amount of the battery under test according to the data.

[0015] The present invention also provides a method for correcting the dynamic characteristics of a differential power compensation type battery isothermal calorimeter, including the following steps:

[0016] Step 1. Determine the model of the battery under test, and select a reference battery of the same model and the same size as the battery under test.

[0017] Step 2. According to the size of the battery under test, select appropriate flexible heating sheets, heat spreading blocks, and thermal conductive silicone pads, and install the sample side and the reference side in the heat sinks of the isothermal calorimetric chamber respectively. Among them, from top to bottom on the sample side are the thermal conductive silicone pad, the heat spreading block, the flexible heating sheet, the battery under test, the flexible heating sheet, the heat spreading block, and the thermal conductive silicone pad. From top to bottom on the reference side are the thermal conductive silicone pad, the heat spreading block, the flexible heating sheet, the reference battery, the flexible heating sheet, the heat spreading block, and the thermal conductive silicone pad.

[0018] Step 3. Install the temperature sensors in the grooves on the sides of the sample side and the reference side heat spreading blocks close to the battery, and connect the sample side flexible heating sheets in parallel to an external constant current and constant voltage source device. After installation, seal the isothermal calorimetric chamber.

[0019] Step 4. Determine the charge and discharge parameters and the target temperature of the battery under test.

[0020] Step 5. Start the calorimeter, control the temperature of the heat sink to a constant temperature point lower than the target temperature. After the temperature in the calorimetric chamber is stable, control the temperatures of the sample side and the reference side heat spreading blocks to the target temperature to keep the output power of the flexible heating sheet and the temperature of the heat spreading block stable.

[0021] Step 6. Perform charge and discharge operations on the battery under test, control the temperature of the sample-side heat spreader to be stable at the target temperature, use the temperature of the reference-side heat spreader as the reference temperature, and through feedback control of the temperature sensor, make the temperature of the sample-side heat spreader consistent with that of the reference side, and record the power changes of the flexible heating sheets on the sample side and the reference side during the charge and discharge process;

[0022] Step 7. Calculate the power change rate using the battery heat generation power, add the limiting condition of continuity at the specified point, and perform piecewise fitting of the power change rate by polynomial piecewise fitting to obtain the heat generation power and power change rate after fitting;

[0023] Step 8. Calculate the time constant using the charge and discharge data, substitute the measured battery heat generation power, time constant, and power change rate into the calibration formula to obtain the corrected battery heat generation power, and complete the dynamic characteristic correction;

[0024] Step 9. Use the power of the reference-side heating sheet as the baseline power, calculate the difference between the powers of the sample-side and reference-side heating sheets to obtain the real-time heat generation power during the charge and discharge process of the battery under test;

[0025] Step 10. Integrate the real-time heat generation power of the battery under test with respect to time to obtain the heat generation amount during the charge and discharge process of the battery.

[0026] In summary, to reduce the influence of environmental temperature fluctuations on the baseline power, the present invention designs a differential power compensation type battery isothermal calorimeter to make the baseline power more in line with the actual situation, and proposes a dynamic characteristic correction method for the battery isothermal calorimeter based on piecewise polynomial fitting, which improves the accuracy of the measurement of the heat generation during the charge and discharge of the battery, and is easy to operate and has lower cost, providing technical support for the accurate measurement of the thermal characteristics of lithium-ion batteries. Brief Description of the Drawings

[0027] Figure 1 is a schematic diagram of the installation of the calorimetry core device of the present invention;

[0028] Figure 2 is the equivalent heat transfer model of the sample side and the reference side;

[0029] Figure 3 is a curve graph of the power change rate versus time before and after fitting during the charging experiment of a 53Ah ternary lithium battery;

[0030] Figure 4 is a curve graph of the power change rate versus time before and after fitting during the discharging experiment of a 53Ah ternary lithium battery;

[0031] Figure 5 is a curve graph of the heat generation power versus time before and after fitting during the charging experiment of a 53Ah ternary lithium battery;

[0032] Figure 6It is a curve graph of the heat generation power of a 53Ah ternary lithium battery during discharge experiment before and after fitting with respect to time;

[0033] Figure 7 It is the power curve of the calorimeter and the constant current source during the calibration experiment of the traditional power compensation type;

[0034] Figure 8 It is the power curve of the calorimeter and the constant current source during the calibration experiment of the present invention;

[0035] In the figure: 1. Reference side battery; 2. Sample side battery; 3. Flexible heating sheet; 4. Temperature sensor; 5. Heat equalizing block; 6. Thermal conductive silica gel pad; 7. Heat sink; 8. Charge and discharge wire; 9. Oil bath pipeline; 10. Calorimetry chamber; 11. High airtightness aviation plug; 12. Gas flowmeter; 13. Intake valve; 14. Exhaust valve; 15. Pressure relief valve. Detailed implementation manners

[0036] To make the steps, technical solutions and advantages of the embodiments of the present invention clearer, the following will combine the accompanying drawings in the embodiments of the present invention to describe the technical solutions in the embodiments of the present invention more clearly, in detail and completely. The following embodiments are used to illustrate the present invention, but are not used to limit the scope of the present invention.

[0037] The present invention aims to solve the problems that the baseline power of the isothermal calorimeter based on the power compensation method is easily interfered by environmental temperature fluctuations, resulting in excessive noise, and the problem of the fitting accuracy of the power curve. Accordingly, the present invention designs a differential power compensation type battery isothermal calorimeter and a dynamic characteristic correction method.

[0038] As Figure 1 shown, the structure of a differential power compensation type battery isothermal calorimeter of the present application is as follows:

[0039] According to the geometric dimensions of the selected sample side battery 2 and the reference side battery 1 of the same model and the same size, the corresponding flexible heating sheet 3, heat equalizing block 5 and thermal conductive silica gel pad 6 are selected. The side where the battery to be tested is installed is the sample side, and the side where the reference battery is installed is the reference side. On the sample side, it is installed in the heat sink 7 of the isothermal calorimetry chamber 10 in the structure of thermal conductive silica gel pad - heat equalizing block - flexible heating sheet - sample side battery - flexible heating sheet - heat equalizing block - thermal conductive silica gel pad from top to bottom; on the reference side, it is installed in the heat sink of the isothermal calorimetry chamber in the structure of thermal conductive silica gel pad - heat equalizing block - flexible heating sheet - reference side battery - flexible heating sheet - heat equalizing block - thermal conductive silica gel pad from top to bottom. The calorimetry chamber 10 is also equipped with a gas flowmeter 12, an intake valve 13, an exhaust valve 14 and a pressure relief valve 15.

[0040] Furthermore, since installing the thermal conductive silica gel pad, heat equalizing block and graphite pad can reduce the contact thermal resistance between the battery and the constant temperature heat sink and improve the temperature uniformity.

[0041] Further, based on the least squares method, during the solution process of polynomials for different segments, a constraint condition of a specified point is added. Through the addition and solution of this condition, the fitting curves of polynomials for different segments are made continuous at the specified position.

[0042] Further, by changing the input constraint conditions, the continuity at any position of the curve can be restricted. It can be not only used for piecewise fitting at the endpoints, but also for fitting of specified cross data points with cross power data.

[0043] Further, the installation structures on the sample side and the reference side are symmetric.

[0044] Further, to reduce measurement errors, the installation structure on the sample side should be symmetric with the installation structure on the reference side. According to the model of the battery to be measured and the charge and discharge parameters, a charge and discharge wire 8 with an appropriate wire diameter is selected. The positive and negative electrodes of the battery to be measured are connected to external equipment through wires and high-airtightness aviation plugs 11. The temperature sensor 4 is installed in the groove on the side of the upper and lower heat equalizing blocks close to the battery, and it should fit well with the groove. The refrigerant heat sink is connected to an external oil bath through an oil bath pipeline 9. After the installation is completed, the calorimeter chamber is closed.

[0045] Further, connecting the battery charge and discharge wires in a four-wire system can reduce the influence of line impedance on the accuracy of experimental data.

[0046] Based on the above device, the following gives a method for correcting the dynamic characteristics of a differential power compensation type battery isothermal calorimeter:

[0047] After checking that the device installation and line connection are correct, start the isothermal calorimeter. The oil bath temperature is set to the external circulation temperature control mode, and the temperature of the heat sink is controlled to a constant temperature point lower than the target temperature; if the target temperature is above room temperature, there is no need for an oil bath. After the temperature of the heat sink is stable, the temperature control system controls the temperatures of the heat equalizing blocks on the sample side and the reference side to the target temperature. Run for a period of time and wait until the output power of the flexible heating sheet and the temperature of the heat equalizing block are stable. Use the battery charge and discharge equipment to charge and discharge the battery to be measured according to the preset charge and discharge parameters. During this process, keep the temperature of the heat equalizing block on the sample side stable at the target temperature, and use the temperature of the heat equalizing block on the reference side as the reference temperature, so that the temperature of the heat equalizing block on the sample side is the same as the reference temperature on the reference side. Use the output power of the heating sheet on the reference side during the charge and discharge process as the baseline power.

[0048] During the experiment, use the upper computer software to collect and record the real-time output powers of the heating sheets on the sample side and the reference side of the battery isothermal calorimeter. After the battery charge and discharge is completed, analyze the charge and discharge parameters, extract the heat generation power, the change rate of heat generation power, and the time constant, etc. from the experimental data, and then perform piecewise fitting on the change rate of heat generation power polynomial by adding the constraint condition of being continuous at the specified point, so as to complete the correction of the dynamic characteristics of the battery isothermal calorimeter.

[0049] Calculate the heat generation power and heat generation amount during the charge and discharge process of the sample-side battery: The real-time heat generation power during the charge and discharge process of the sample-side battery is obtained according to formula (1), and the heat generation amount of the battery to be measured is obtained from formula (2).

[0050]

[0051]

[0052] Where is the real-time heat generation power of the sample-side battery during the charge and discharge process; is the real-time output power of the reference-side heating sheet; is the real-time output power of the sample-side heating sheet; is t 1 to t 2 is the heat generation amount of the sample-side battery during the time period; t 1 is the starting time point of the charge and discharge of the sample-side battery; t 2 is the time point when the system returns to stability after the charge and discharge of the sample-side battery ends.

[0053] The principle of piecewise polynomial fitting will be described in detail below, and the idea of the piecewise polynomial fitting method is expressed as follows:

[0054] For the battery charge and discharge data points ( , , … ) and their corresponding heat generation power values are ( , , … ), the order of polynomial fitting is m, an n×m matrix can be established according to the least squares method. In order to make the fitted curve continuous with the previous fitted curve at the specified point, it is necessary to add a constraint condition to the curve to be fitted. The specific constraint conditions include the data coordinates of the specified point and the derivative at that point, ensuring that the derivatives of the data points and the segmentation points are consistent, and it can be considered that the two ends of the fitted curve are continuous. By adding the constraint conditions, the continuity of the fitted function at the interval segmentation point is ensured.

[0055] Furthermore, for a section of battery charge and discharge data with n points ( , , … ), its corresponding power values during battery charge and discharge are ( , , … ), and the following two formulas are established:

[0056]

[0057]

[0058] wherein to are the polynomial coefficients to be fitted, Equation (3) is the polynomial function after fitting, and Equation (4) is the derivative of Equation (3). i.e., ( , … ) is the corresponding derivative value of the battery charge and discharge power value, i.e., the power change rate.

[0059] The calculation method of the power change rate can be simplified to the change rate of the data values before and after the point to be calculated, and the following formula can be established:

[0060]

[0061] For the expected curve after fitting, through specific limit points ( , ), the following two formulas can be established:

[0062]

[0063]

[0064] Equation (6) indicates that the curve after fitting passes through the point ( , ), and Equation (7) indicates that the derivative of the curve after fitting at this point is a set value. By restricting the curve through Equation (6) and Equation (7), the fitting curves of different segments are continuously and smoothly connected at the limit points.

[0065] For Equation (3) and Equation (6), subtracting the two equations gives:

[0066]

[0067] Furthermore, let Equation (7) × to obtain:

[0068]

[0069] Furthermore, subtracting Equation (8) from Equation (9) gives:

[0070]

[0071] For Equation (10), there exist , , … There are n power values ​​in total, which can form n equations, which can be converted into the form of matrix multiplication:

[0072]

[0073] By solving the above matrix, we can obtain to The value of .

[0074] Will to Substituting the value of back into formula (7), we can get , and then to Substituting the value of back into formula (6), we can get , so far the polynomial coefficients to After the coefficients are completely obtained, the fitted values ​​can be obtained by substituting them into formula (3).

[0075] In one embodiment, the above method is implemented in Matlab software, and the constructor , is the charging and discharging time and power value of the battery to be fitted, To limit the value of the fitting curve at this point, To limit the derivative of the fitting curve at this point, n is the order of the fitting polynomial, are the P value and its derivative value of the fitted curve respectively.

[0076] The simplified first-order calibration formula of the non-steady-state heat transfer equation of the battery isothermal calorimetry core system is:

[0077]

[0078] in is the corrected battery heat generation power, is the heat generation power of the battery measured by the instrument, is the time constant, is the power change rate, Related to the thermal capacity of the battery and the thermal resistance between the battery and the heater.

[0079] The above method is used to correct the dynamic characteristics of the battery isothermal calorimeter. The parameters of the battery to be tested are shown in Table 1.

[0080] Table 1 Test parameters of battery charge and discharge

[0081]

[0082] Figure 3The graph shows the change rate of the heat generation power of the battery over time when charging the battery isothermal calorimeter. Curve 1 is the measured curve and curve 2 is the corrected curve. Figure 4 The graph shows the change rate of the heat generation power of the battery over time when discharging the battery isothermal calorimeter. Curve 1 is the measured curve and curve 2 is the corrected curve. From Figure 3 and Figure 4 it can be seen from the measured curves that there is significant noise in the directly calculated power change rate, so fitting is required. During the battery charging process, the data is divided into 16 segments, and during the battery discharging process, the data is divided into 15 segments. Each segment of data has cross-sample points with the front and rear ends. By adjusting the order and restricting continuous points, and removing the redundant cross-sample curves, the corrected continuous piecewise fitting curve is obtained, that is, Figure 3 and Figure 4 the corrected curves in

[0083] Using the measured heat generation power curve of the battery isothermal calorimeter during discharging, the time constant is obtained as 318 s. According to Equation (11), the corrected power value at each moment can be obtained. Figure 5 The graph shows the heat generation power of the battery over time when charging the battery isothermal calorimeter. Curve 1 is the measured curve and curve 2 is the corrected curve; Figure 6 The graph shows the heat generation power of the battery over time when discharging the battery isothermal calorimeter. Curve 1 is the measured curve and curve 2 is the corrected curve. Table 2 shows the heat generation data of the lithium battery during charging and discharging before and after the dynamic characteristic correction of the isothermal calorimeter.

[0084] Table 2 Heat generation of the battery during charging and discharging before and after the dynamic characteristic correction of the isothermal calorimeter

[0085]

[0086] The correction results show that a method for correcting the dynamic characteristics of a battery isothermal calorimeter based on piecewise polynomial fitting proposed in the embodiments of the present application greatly improves the thermal hysteresis phenomenon of the isothermal calorimeter and at the same time ensures the accuracy of the heat generation data of the battery during charging and discharging.

[0087] Next, the structures of the sample side and the reference side will be analyzed, and a detailed mathematical model will be derived by constructing their equivalent circuit diagrams.

[0088] For Figure 1 the structure of the isothermal calorimeter described above, the equivalent circuit diagram of the heat transfer model on the sample side is as shown in Figure 2 the sample side, where T is temperature, C is heat capacity, and R is thermal resistance; the subscript b represents the battery, h represents the heater, a represents the heat equalizing block, and s represents the heat sink; is the heat generation power of the battery to be measured; is the output power of the heating sheet on the sample side; R bhis the sum of the thermal resistances of the heater and the battery; R ha is the sum of the thermal resistances of the heater and the heat spreader; R as is the sum of the thermal resistances of the heat spreader and the heat sink.

[0089] For the battery on the sample side, its thermal energy change consists of two parts. One part is the thermal power generated or absorbed during the charge and discharge process, and the other part is the heat transfer power through conduction with the heating sheet. The equation for the thermal energy change of the battery on the sample side is shown in Equation (13):

[0090]

[0091] The first term on the right side of Equation (13) represents the heat generation power of the battery on the sample side, and the second term represents the heat exchange power between the battery and the heater.

[0092] For the heating sheet, its thermal energy change also consists of two parts. One part is the Joule heat power converted from electrical energy, and the other part is the heat transfer power through conduction with the heat spreader and the battery on the sample side. The equation for the thermal energy change of the heating sheet on the sample side is shown in Equation (14):

[0093]

[0094] The first term on the right side of Equation (14) represents the heat generation power of the heater, the second term represents the heat exchange power between the heater and the heat spreader, and the third term represents the heat exchange power between the heater and the battery.

[0095] Since there is no internal heat source in the heat spreader on the sample side, the equation for the thermal energy change is shown in Equation (15). The two terms on the right side of the equation are the heat transfer powers through conduction between the heat spreader and the heat sink, and between the heat spreader and the heater, respectively:

[0096]

[0097] By combining Equations (13), (14), and (15), the equation for the total thermal energy change on the sample side is obtained:

[0098]

[0099] Integrating both sides of Equation (16) with respect to time, since the temperatures of all components remain unchanged before and after charge and discharge, Equation (16) can be transformed into Equation (17).

[0100]

[0101] From Equation (17), it can be seen that under ideal conditions, it is considered that the temperature of the heat sink and the temperature of the heat spreader remain constant, and the heat transfer power through conduction between the heat spreader and the heat sink is constant, which is the baseline power on the sample side. This power is composed of the heat absorption and release power of the battery and the compensation power of the heating sheet Maintained by linearly fitting the output power of the heating sheet against time before and after charge and discharge. However, in actual situations, the temperature of the heat equalizing block is vulnerable to fluctuations in the ambient temperature, resulting in high baseline power noise on the sample side. Therefore, the output power of the heating sheet on the reference side is used as the real-time baseline power to reduce the environmental impact.

[0102] For Figure 1 the structure of the isothermal calorimeter described, the equivalent circuit diagram of the heat transfer model on the reference side is as Figure 2 shown on the reference side. The structures of the sample side and the reference side are the same, and it can be considered that the heat capacities and thermal resistances on both sides are equal. Here, the superscript "'" represents the reference side; T is temperature, C is heat capacity, R is thermal resistance; the subscript b represents the battery, h represents the heater, a represents the heat equalizing block, and s represents the heat sink; is the output power of the heating sheet on the reference side.

[0103] The reference battery is not connected to an external battery charge and discharge tester, so there is no internal heat source, and thus its heat generation power is 0. The heat energy change equation of the reference battery is as shown in formula (18):

[0104]

[0105] The heat energy change equation of the heating sheet on the reference side is as shown in formula (19):

[0106]

[0107] The heat energy change equation of the heat equalizing block on the reference side is as shown in formula (20):

[0108]

[0109] Combining formulas (18), (19), and (20), the total heat energy change equation of the reference side is obtained:

[0110]

[0111] It can be seen from formula (21) that the heat conduction power between the heat equalizing block and the heat sink on the reference side is maintained by the output power of the heating sheet. The power of the heating sheet on the reference side can be used as the baseline power.

[0112] During the experiment, the temperature of the heat sink on the sample side is equal to the temperature of the heat sink on the reference side . By the temperature control system, the temperature of the heat equalizing block on the sample side is kept consistent with the reference temperature on the reference side . Therefore, it can be seen from formulas (17) and (21) that the baseline power on the reference side can be used as the baseline power on the sample side, that is, formula (22).

[0113]

[0114] Then the real-time heat generation power formula (23) of the battery on the sample side can be obtained:

[0115]

[0116] Integrating the real-time heat generation power of the battery on the sample side with respect to time gives the heat generation amount of the battery during charge and discharge , as shown in formula (24):

[0117]

[0118] Using the above method, a calibration experiment is carried out.

[0119] Figure 7 are the power curves of the traditional power compensation calorimeter and the constant current source in the calibration experiment. Figure 8 are the power curves of the calorimeter and the constant current source in the calibration experiment of this application, that is, the differential power compensation calorimeter. It can be seen from Figure 7 and Figure 8 that this application makes up for the shortcomings of the battery isothermal calorimeter that the baseline is easily affected by environmental temperature fluctuations, resulting in large power noise; at the same time, compared with the heat flow method isothermal calorimeter, the operation is more convenient, the measurement efficiency is improved; and there is no need for an oil bath device above room temperature. While having the advantages of the isothermal calorimeter, the present invention improves the accuracy of battery thermal characteristic measurement, ensures the measurement efficiency, and has a lower cost.

Claims

1. A method for correcting dynamic characteristics of a differential power compensation battery isothermal calorimeter, characterized in that: The following steps are involved: Step 1. Determine the model of the battery to be tested, and select a reference battery of the same model and size as the battery to be tested; Step 2. According to the size of the battery to be tested, select the appropriate flexible heating sheet, uniform heating block and thermally conductive silicone pad, and install the sample side and the reference side in the heat sink of the isothermal calorimetry chamber respectively, wherein the sample side is, from top to bottom, a thermally conductive silicone pad, a uniform heating block, a flexible heating sheet, a battery to be tested, a flexible heating sheet, a uniform heating block, and a thermally conductive silicone pad, and the reference side is, from top to bottom, a thermally conductive silicone pad, a uniform heating block, a flexible heating sheet, a reference battery, a flexible heating sheet, a uniform heating block, and a thermally conductive silicone pad; Step 3. Install the temperature sensor in the groove of the sample side and reference side heat block close to the battery side, and connect the sample side flexible heating sheet in parallel with the external constant current and constant voltage source equipment. After the installation is completed, seal the isothermal calorimetric cavity; Step 4. Determine the charge and discharge parameters and target temperature of the battery to be tested; Step 5. Start the calorimeter, control the temperature of the heat sink to a constant temperature point lower than the target temperature, and after the temperature of the calorimetric chamber is stable, control the temperature of the sample side and the reference side uniform heating block to the target temperature, so that the output power of the flexible heating sheet and the temperature of the uniform heating block remain stable; Step 6. Perform charge and discharge operations on the battery to be tested, control the temperature of the sample side uniform heating block to be stable at the target temperature, and use the temperature of the reference side uniform heating block as the reference temperature. The temperature of the sample side uniform heating block is kept consistent with that of the reference side through temperature sensor feedback control, and record the power changes of the flexible heating sheets on the sample side and the reference side during the charge and discharge process; Step 7. Calculate the power change rate using the heat generation power of the battery, add a continuous restriction condition at the specified point, fit the power change rate through polynomial piecewise fitting, and obtain the fitted heat generation power and power change rate; Step 8. Use the charge and discharge data to obtain the time constant, substitute the measured battery heat generation power, time constant and power change rate into the calibration formula to obtain the corrected battery heat generation power, and complete the dynamic characteristic correction; Step 9. Taking the power of the reference side heater as the baseline power, the difference between the power of the sample side heater and the power of the reference side heater is calculated to obtain the real-time heat generation power during the charge and discharge process of the battery to be tested; Step 10. Integrate the real-time heat generation power of the battery to be tested over time to obtain the heat generation during the battery charging and discharging process.

2. The method for correcting dynamic characteristics of a differential power compensation battery isothermal calorimeter according to claim 1, characterized in that: The polynomial segmented fitting in step 7 is based on the least square method, and continuity constraints of specified points are added during the fitting process to ensure smooth transition of the fitting curve at the segmented points.

3. The method for correcting dynamic characteristics of a differential power compensation battery isothermal calorimeter according to claim 1 or 2, characterized in that: The calibration formula in step 8 is: Where P 修正 is the corrected battery heat generation power, P 测量 is the heat generation power of the battery measured by the instrument, τ is the time constant, is the power change rate.

4. The method for correcting dynamic characteristics of a differential power compensation battery isothermal calorimeter according to claim 3, characterized in that: The real-time heat generation power calculation formula in step 9 is: q b =q r -q s where q b is the real-time heat generation power of the battery under test during the charging and discharging process; q r is the real-time output power of the reference side heater; q s It is the real-time output power of the heater on the sample side.

5. The method for correcting dynamic characteristics of a differential power compensation battery isothermal calorimeter according to claim 3, characterized in that: The heat generation calculation formula in step 10 is: Where Q is the heat generated by the battery under test during the time period from t1 to t2; t1 is the starting time point of charging and discharging of the battery under test; t2 is the time point when the system returns to stability after the charging and discharging of the battery under test is completed.

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