Differential power compensation type battery isothermal calorimeter and dynamic characteristic correction method

Abstract

The invention discloses a differential power compensation type battery isothermal calorimeter and a dynamic characteristic correction method. A stable temperature boundary is provided by the constant-temperature heat sink, a battery to be measured and a reference battery with the same model and size are mounted in the constant-temperature calorimetric cavity, and the battery to be measured and the reference battery are heated to a target temperature by using the flexible heating sheet. In the process of charging and discharging the to-be-tested battery, the power of the reference side heating sheet is used as the baseline power, the output power of the sample side heating sheet is subjected to feedback control, and the real-time output power of the reference side heating sheet and the sample side heating sheet is collected and recorded. On the basis of curve polynomial piecewise fitting, a limiting condition is added in a fitting curve, the limiting condition is that the curve is continuous at a specified point after fitting, and then a power value and a power change rate value after fitting are obtained. And the real-time heat production power of the to-be-tested battery in the charging and discharging process can be obtained according to the difference value of the two powers, so that the heat production of the battery is calculated through integration. According to the invention, interference caused by environment temperature fluctuation can be reduced, and the baseline power changing in real time can be obtained.

Description

Technical Field

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

[0002] At present, the calorimeters used in the study of heat generation of lithium-ion batteries mainly include adiabatic accelerating calorimeter and isothermal calorimeter. The measurement principle of adiabatic accelerating calorimeter is to keep the temperature of the calorimetric chamber 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, thereby obtaining an adiabatic temperature rise, and finally the heat generation power of the object under test is obtained by calculating the adiabatic temperature rise rate. The measurement principle of isothermal calorimeter is to keep the temperature of the calorimetric chamber 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 through real-time feedback to keep the temperature of the object under test constant, thereby obtaining the heat generation power of the object under test and measuring its heat absorption and release under this temperature condition.

[0003] The adiabatic accelerating calorimeter can simulate the thermal characteristics of the battery exothermic reaction process when the internal heat of the battery cannot be dissipated in time. It has rich and diverse functions and is widely used in the field of battery thermal management. However, it also has the following disadvantages: First, the adiabatic accelerating calorimeter has no refrigeration function and cannot quickly track the temperature of the battery's cooling process, so it is difficult to measure the endothermic effect. Second, due to the thermal hysteresis effect, the instrument cannot enter a true 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 battery charge and discharge heat generation power measurement accuracy is high. Third, the charge and discharge heat generation characteristics of the battery at a certain fixed temperature point can be accurately measured.

[0004] The basic principles of isothermal calorimeters are divided into heat flow method and 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 calorimetric system, and the battery to be tested is heated to the target temperature through the heater. After the temperature stabilizes, the output power of the heater is recorded and used as the baseline power; when the battery starts working, the heat absorption and release effect of the battery causes the sensor temperature to change. The temperature control system controls the heater power through feedback to keep the sensor temperature at the target temperature. The power change of the heater is equivalent to the battery thermal effect. Integrating the heater output power will obtain the heat generated during the battery charging and discharging process. From the working principle, it can be seen that since the heater power controls the battery temperature in real-time feedback, the baseline power of the isothermal calorimeter is easily affected by ambient temperature fluctuations, and the baseline power data during the calorimetric process cannot be directly obtained. It needs to be obtained by linear fitting the heater output power and time before and after charging and discharging, resulting in excessive baseline power noise. The baseline power noise of the common battery isothermal calorimeter based on the power compensation method is greater than 10mW. When the battery capacity is small or the charge and discharge rate is low, the heat generation power of the battery is small, so when the isothermal calorimeter is measuring the heat generation of such batteries during charge and discharge, the measurement result error is large due to noise interference, thereby reducing the reference value of the experimental data.

[0005] The heat generation measurement method of lithium battery charging and discharging based on isothermal differential calorimetry calculates the real-time heat flow of the battery when it is working by measuring the temperature difference between the battery to be tested and the reference battery in the dual chamber. Although it can improve the above problems to a certain extent, it requires obtaining the equivalent heat capacity C and equivalent thermal resistance R of the system, and the experimental steps are relatively complicated.

[0006] In addition, there is inevitably a certain thermal hysteresis effect in the measurement of heat generation power. On the one hand, the heat generated by lithium batteries mainly comes from the core. There is an obvious thermal resistance in the heat transfer path from the core to the battery surface. At the same time, the thermal 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 need to be installed on both sides of the battery before testing, including graphite gaskets, silicone pads and uniform heat blocks. The thermal resistance between the components cannot be ignored. It can be considered that the measurement of battery heat generation power involves a non-steady-state heat transfer process with a delay link. The time lag phenomenon of this process causes the measurement result to be unable to be directly equivalent to the transient heat generation power of the battery.

[0007] Data fitting is an important way to deal with errors and correct curves, and is widely used in the correction of dynamic characteristics of battery isothermal calorimeters. As data processing becomes increasingly complex, polynomial fitting has unique advantages in the field of data fitting due to its convenient calculation method and small error. At present, ordinary polynomial fitting uses a polynomial expansion to fit all observation points in a small analysis area containing several analysis grid points. Among them, the linear least squares method is a common method to solve curve fitting problems. By using a set of simple, suitable, and linearly independent basis functions to approximate experimental data, the 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, the polynomial order is too low, and the fitting accuracy and effect are not ideal. To improve the fitting accuracy and effect, it is necessary to increase the curve order, but too high an order will bring about computational complexity and other disadvantages. Therefore, if only one polynomial curve function is used to fit more data points, it is difficult to achieve good fitting accuracy and effect. Summary of the invention

[0008] In view of the shortcomings of the battery isothermal calorimeter mentioned in the background technology, such as large baseline power noise and deficiencies in dynamic characteristics, the present invention designs a differential power compensation type battery isothermal calorimeter, and proposes a dynamic characteristic correction method of the battery isothermal calorimeter based on piecewise polynomial fitting. The present invention can reduce the interference caused by ambient temperature fluctuations, obtain real-time changing baseline power, increase the restriction condition of the piecewise polynomial fitting at the interval segmentation point, realize the dynamic characteristic correction of the battery isothermal calorimeter, thereby improving the accuracy of the heat generation measurement of lithium battery charging and discharging, and making the operation easier; above room temperature, no oil bath device is required, which can reduce costs.

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

[0010] A sample side device is used to install a battery to be tested, the sample side device comprises a sample side heat sink, a sample side heat equalizing block, a sample side flexible heating sheet, a sample side thermally conductive silicone pad and a sample side temperature sensor; the sample side flexible heating sheet, the sample side heat equalizing block and the sample side thermally conductive silicone 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 a groove of the sample side heat equalizing block close to the battery side;

[0011] A reference side device, used for installing a reference battery, the reference side device comprises a reference side heat sink, a reference side uniform heating block, a reference side flexible heating sheet, a reference side thermally conductive silicone pad and a reference side temperature sensor; the reference side flexible heating sheet, the reference side uniform heating block and the reference side thermally conductive silicone pad are sequentially stacked on the reference side heat sink, the reference battery is installed between the reference side flexible heating sheets, and the reference side temperature sensor is installed in a groove of the reference side uniform heating block close to the battery side;

[0012] a calorimetric chamber, used for accommodating a sample side device and a reference side device;

[0013] A temperature control system is used to control the temperature in the calorimetric chamber so that the temperature of the sample side uniform heating block and the temperature of the reference side uniform heating 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 of the battery to be tested based on the data.

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

[0016] 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;

[0017] 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;

[0018] 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;

[0019] Step 4. Determine the charge and discharge parameters and target temperature of the battery to be tested;

[0020] 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;

[0021] 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;

[0022] 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;

[0023] 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;

[0024] 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;

[0025] 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.

[0026] In summary, in order to reduce the impact of ambient temperature fluctuations on baseline power, the present invention designs a differential power compensation battery isothermal calorimeter to make the baseline power more realistic, and proposes a dynamic characteristic correction method for a battery isothermal calorimeter based on piecewise polynomial fitting, which improves the accuracy of battery charge and discharge heat generation measurement, is easy to operate, and has lower cost, providing technical support for accurate measurement of thermal characteristics of lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

[0030] Figure 4 This is a curve diagram of the power change rate of the 53Ah ternary lithium battery discharge experiment before and after fitting;

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

[0032] Figure 6This is a curve diagram of the heat generation power of a 53Ah ternary lithium battery discharge experiment changing with time before and after fitting;

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

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

[0035] In the figure: 1. Reference side battery; 2. Sample side battery; 3. Flexible heating plate; 4. Temperature sensor; 5. Uniform heating block; 6. Thermal conductive silicone pad; 7. Heat sink; 8. Charging and discharging wires; 9. Oil bath pipeline; 10. Calorimetric chamber; 11. High airtightness aviation plug; 12. Gas flow meter; 13. Inlet valve; 14. Outlet valve; 15. Pressure relief valve. DETAILED DESCRIPTION

[0036] In order to make the steps, technical solutions and advantages of the implementation examples of the present invention clearer, the following will be combined with the drawings in the implementation examples of the present invention to describe the technical solutions in the implementation of the present invention in a clearer, detailed and complete manner. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

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

[0038] like Figure 1 As shown, the structure of a differential power compensation 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 size, the corresponding flexible heating sheet 3, uniform heating block 5 and thermally conductive silicone 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. The sample side is installed in the heat sink 7 of the isothermal calorimetric chamber 10 in the structure of thermally conductive silicone pad-uniform heating block-flexible heating sheet-sample side battery-flexible heating sheet-uniform heating block-thermal conductive silicone pad from top to bottom; the reference side is installed in the heat sink of the isothermal calorimetric chamber in the structure of thermally conductive silicone pad-uniform heating block-flexible heating sheet-reference side battery-flexible heating sheet-uniform heating block-thermal conductive silicone pad from top to bottom. The calorimetric chamber 10 is also equipped with a gas flow meter 12, an air inlet valve 13, an air outlet valve 14 and a pressure relief valve 15.

[0040] Furthermore, the installation of thermally conductive silicone pads, heat-distributing blocks and graphite pads can reduce the contact thermal resistance between the battery and the constant temperature heat sink, and improve temperature uniformity.

[0041] Furthermore, based on the least square method, in the process of solving the polynomials of different segments, the restriction condition of the specified point is added, and by adding and solving the condition, the polynomial fitting curves of different segments are made continuous at the specified position.

[0042] Furthermore, by changing the input restriction conditions, the continuity at any position of the curve can be restricted, which can be used not only for piecewise fitting at the endpoints, but also for fitting of specified cross data points where cross power data exist.

[0043] Furthermore, the sample side and the reference side are mounted in a symmetrical structure.

[0044] Furthermore, in order to reduce the measurement error, the sample side installation structure should be symmetrical with the reference side installation structure. According to the battery model and charge and discharge parameters to be tested, select the charge and discharge wire 8 with a suitable wire diameter, and connect the positive and negative electrodes of the battery to be tested to the external device through the wire and the high-airtightness aviation plug 11. Install the temperature sensor 4 in the groove close to the battery side of the upper and lower heat blocks, and fit well with the groove. The heat sink with refrigerant is connected to the external oil bath through the oil bath pipe 9, and the calorimetric chamber is closed after the installation is completed.

[0045] Furthermore, connecting the battery charging and discharging 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 dynamic characteristics correction method of the differential power compensation battery isothermal calorimeter is given below:

[0047] After checking that the device is installed and the line connection is correct, start the isothermal calorimeter, set the oil bath temperature to the external circulation temperature control mode, and control the heat sink temperature to a constant temperature point lower than the target temperature; if the target temperature is above room temperature, no oil bath is required. After the heat sink temperature stabilizes, the temperature control system controls the temperature of the sample side and reference side uniform heating blocks to the target temperature. Run for a while and wait for the output power of the flexible heating plate and the temperature of the uniform heating block to remain stable. Use the battery charging and discharging equipment to charge and discharge the battery to be tested according to the preset charging and discharging parameters. During this process, keep the temperature of the sample side uniform heating block stable at the target temperature, and use the temperature of the reference side uniform heating block as the reference temperature, so that the temperature of the sample side uniform heating block is consistent with the reference temperature of the reference side, and use the output power of the reference side heating plate during the charging and discharging process as the baseline power.

[0048] During the experiment, the host computer software was used to collect and record the real-time output power of the heating plates on the sample and reference sides of the battery isothermal calorimeter. After the battery was charged and discharged, the charging and discharging parameters were analyzed. The heat generation power, heat generation power change rate, and time constant were extracted from the experimental data. Then, the heat generation power change rate polynomial was fitted piecewise by adding continuous restrictions at specified points, thereby completing the correction of the dynamic characteristics of the battery isothermal calorimeter.

[0049] The heat generation power and heat generation during the charging and discharging process of the sample side battery are calculated: the real-time heat generation power during the charging and discharging process of the sample side battery is obtained according to formula (1), and the heat generation of the battery to be tested is obtained according to formula (2).

[0050]

[0051]

[0052] in The real-time heat generation power of the sample side battery during the charging and discharging process; is the real-time output power of the reference side heating plate; The real-time output power of the sample side heater; is the heat generated by the battery on the sample side during the time period from t1 to t2; t1 is the starting time point of charging and discharging of the battery on the sample side; t2 is the time point when the system returns to stability after the charging and discharging of the battery on the sample side is completed.

[0053] The following will explain the principle of piecewise polynomial fitting in detail. The idea of ​​piecewise polynomial fitting method is as follows:

[0054] For the battery charge and discharge data points ( , , … ) and its corresponding heat generation power value is ( , , … ), the polynomial fitting order is m, and an n×m matrix can be established by the least squares method. In order to make the fitted curve continuous with the previous fitting curve at the specified point, it is necessary to add restrictions to the curve to be fitted. The specific restrictions include the data coordinates of the specified point and the derivative of the point. If the derivatives of the data point and the segmentation point are consistent, the fitting curves at both ends can be considered continuous. By adding restrictions, the continuity of the fitting function at the segmentation points of the interval is guaranteed.

[0055] Furthermore, for a battery charging and discharging data with n points ( , , … ), the corresponding power value of the battery during charging and discharging is ( , , … ), establish the following two formulas:

[0056]

[0057]

[0058] in to are the polynomial coefficients to be fitted, formula (3) is the polynomial function after fitting, and formula (4) is the derivative of formula (3). Right now( , … ) is the derivative value corresponding to the battery charging and discharging power value, that is, the power change rate.

[0059] The power change rate calculation method 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 desired fitting curve, it can pass through specific limiting points ( , ), the following two formulas can be established:

[0062]

[0063]

[0064] Formula (6) shows that the curve after fitting passes through ( , ) point, formula (7) indicates that the derivative of the fitted curve at this point is the set value. The curve is limited by formulas (6) and (7) so that the fitting curves of different segments are continuously and smoothly connected at the limited points.

[0065] For formula (3) and formula (6), the difference between the two formulas is:

[0066]

[0067] Further, let formula (7) × We can get:

[0068]

[0069] Furthermore, by subtracting formula (8) from formula (9), we can obtain:

[0070]

[0071] For formula (10), there exists , , … 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 3 This is a graph showing the rate of change of heat generation power of the battery over time when the battery isothermal calorimeter is charging, where curve 1 is the measured curve and curve 2 is the corrected curve. Figure 4 The graph is a graph showing the rate of change of heat generation power of the battery over time during discharge of the battery isothermal calorimeter, where curve 1 is the measured curve and curve 2 is the corrected curve. Figure 3 and Figure 4 It can be seen from the measured curve that the power change rate obtained by direct calculation has large noise, so fitting is required. The data is divided into 16 segments during battery charging and 15 segments during battery discharging. Each segment of data has cross sample points with the front and rear end outputs. By adjusting the order and limiting continuous points, and removing redundant cross sample curves, the modified continuous segmented fitting curve is obtained, that is, Figure 3 and Figure 4 The correction curve in .

[0083] The discharge heat generation power curve was measured using a battery isothermal calorimeter to obtain the time constant According to formula (11), the corrected power value at each moment can be obtained. Figure 5 It is a curve diagram of the heat generation power changing with time when the battery isothermal calorimeter is charging, where curve 1 is the measured curve and curve 2 is the corrected curve; Figure 6 The graph is a graph showing the heat generation power changing with time when the battery isothermal calorimeter is discharged, where curve 1 is the measured curve and curve 2 is the corrected curve. Table 2 shows the heat generation data of lithium battery charging and discharging before and after the dynamic characteristics of the isothermal calorimeter are corrected.

[0084] Table 2 Battery charge and discharge heat generation before and after correction of the dynamic characteristics of the isothermal calorimeter

[0085]

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

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

[0088] for Figure 1 The equivalent circuit diagram of the sample side heat transfer model of the isothermal calorimeter structure is as follows: Figure 2 As shown on the sample side, T is temperature, C is heat capacity, R is thermal resistance; subscript b represents battery, h represents heater, a represents heat block, and s represents heat sink; The heat generation power of the battery under test; R is the output power of the sample side heater; bh is the thermal resistance of the heater and the battery; R ha is the thermal resistance of the heater and the heat block; R as is the thermal resistance of the heat block and the heat sink.

[0089] For the battery on the sample side, its thermal energy change consists of two parts: one is the heat power generated or absorbed during the charging and discharging process, and the other is the heat conduction and heat exchange power with the heating plate. The thermal energy change equation of the battery on the sample side is shown in formula (13):

[0090]

[0091] The first term on the right side of formula (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 plate, its thermal energy change is also composed of two parts, one part comes from the Joule heat power of electrical energy conversion, and the other part is the heat conduction heat exchange power with the uniform heating block and the battery on the sample side. The thermal energy change equation of the heating plate on the sample side is shown in formula (14):

[0093]

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

[0095] There is no internal heat source in the sample side uniform heating block, so the heat energy change equation is shown in formula (15). The two terms on the right side of the formula are the heat conduction heat transfer power between the uniform heating block and the heat sink, and between the uniform heating block and the heater, respectively:

[0096]

[0097] Combining equations (13), (14) and (15), we can obtain the total heat energy change equation on the sample side:

[0098]

[0099] Integrate both sides of formula (16) with respect to time. Since the temperature of each component remains unchanged before and after charging and discharging, formula (16) can be transformed into formula (17).

[0100]

[0101] From formula (17), we can see that under ideal conditions, the heat sink temperature is and uniform heating block temperature Keep constant, the heat conduction power between the uniform heating block and the heat sink is constant, which is the baseline power on the sample side. This power is determined by the heat absorption and release power of the battery. And the heating plate compensation power Maintain, through the heating plate output power and time linear fitting before and after charging and discharging. But in actual situation, the temperature of the uniform heating block It is easily affected by ambient temperature fluctuations, resulting in large baseline power noise on the sample side. Therefore, the output power of the reference side heater is used as the real-time baseline power to reduce environmental impact.

[0102] for Figure 1 The equivalent circuit diagram of the heat transfer model of the reference side of the isothermal calorimeter structure is as follows: Figure 2 As shown in the reference side, the sample side has the same structure as the reference side, and the heat capacity and thermal resistance on both sides can be considered equal, where the superscript "'" represents the reference side; 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 uniform heat block, and s represents the heat sink; Output power for the reference side heater.

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

[0104]

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

[0106]

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

[0108]

[0109] Combining equations (18), (19) and (20), we can obtain the total heat energy change equation on the reference side:

[0110]

[0111] From formula (21), it can be seen that the heat conduction power between the reference side uniform heating block and the heat sink is maintained by the output power of the heating plate. as the baseline power.

[0112] During the experiment, the temperature of the heat sink on the sample side and the reference side heat sink temperature The temperature of the sample side heating block is kept equal by the temperature control system Reference temperature on the reference side Therefore, from formulas (17) and (21), we can know 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 of the sample side battery can be obtained (23):

[0115]

[0116] The heat generated by the battery during the charge and discharge process can be obtained by integrating the real-time heat generation power of the sample side battery with time. , as shown in formula (24):

[0117]

[0118] Using the above method, a calibration experiment was performed.

[0119] Figure 7 The power curves of a conventional power-compensated calorimeter and a constant current source in a calibration experiment. Figure 8 This is the power curve of the calorimeter and the constant current source in the calibration experiment of the differential power compensation calorimeter of the present application. Figure 7 and Figure 8 It can be seen that this application makes up for the disadvantage that the baseline of the battery isothermal calorimeter is easily affected by ambient temperature fluctuations, resulting in large power noise; at the same time, compared with the heat flow method isothermal calorimeter, the operation is simpler and the measurement efficiency is improved; and no oil bath device is required above room temperature. While combining the advantages of the isothermal calorimeter, the present invention improves the accuracy of the battery thermal characteristic measurement, ensures the measurement efficiency, and has lower cost.

Claims

1. A differential power compensation battery isothermal calorimeter, characterized in that: include: A sample side device is used to install a battery to be tested, the sample side device comprises a sample side heat sink, a sample side heat equalizing block, a sample side flexible heating sheet, a sample side thermally conductive silicone pad and a sample side temperature sensor; the sample side flexible heating sheet, the sample side heat equalizing block and the sample side thermally conductive silicone 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 a groove of the sample side heat equalizing block close to the battery side; A reference side device, used for installing a reference battery, the reference side device comprises a reference side heat sink, a reference side uniform heating block, a reference side flexible heating sheet, a reference side thermally conductive silicone pad and a reference side temperature sensor; the reference side flexible heating sheet, the reference side uniform heating block and the reference side thermally conductive silicone pad are sequentially stacked on the reference side heat sink, the reference battery is installed between the reference side flexible heating sheets, and the reference side temperature sensor is installed in a groove of the reference side uniform heating block close to the battery side; a calorimetric chamber, used for accommodating a sample side device and a reference side device; A temperature control system is used to control the temperature in the calorimetric chamber so that the temperature of the sample side uniform heating block and the temperature of the reference side uniform heating block are maintained at the target temperature; 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 of the battery to be tested based on the data.

2. The differential power compensation battery isothermal calorimeter according to claim 1, characterized in that: The installation structures of the sample side device and the reference side device are symmetrical to ensure measurement accuracy and reduce errors.

3. The differential power compensation battery isothermal calorimeter according to claim 1 or 2, characterized in that: The temperature control system includes an external refrigerant circulation device for providing a constant temperature boundary for the calorimetric system.

4. The differential power compensation battery isothermal calorimeter according to claim 3, characterized in that: The data acquisition and processing system includes a software module for data fitting, which processes the collected power data based on piecewise polynomial fitting to correct dynamic characteristics; adding restriction conditions to the curve to be fitted, the specific restriction conditions include the data coordinates of the specified point and the derivative of the point, ensuring that the derivatives of the data point and the segmentation point are consistent, and by adding the restriction conditions, the continuity of the fitting function at the interval segmentation points is guaranteed.

5. 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.

6. The method for correcting dynamic characteristics of a differential power compensation battery isothermal calorimeter according to claim 5, characterized in that: The polynomial segmented fitting in step 7 is based on the least squares 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.

7. The method for correcting dynamic characteristics of a differential power compensation battery isothermal calorimeter according to claim 5 or 6, characterized in that: The calibration formula in step 8 is: 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.

8. The method for correcting dynamic characteristics of a differential power compensation battery isothermal calorimeter according to claim 7, characterized in that: The real-time heat generation power calculation formula in step 9 is: in The real-time heat generation power of the battery under test during the charging and discharging process; is the real-time output power of the reference side heating plate; It is the real-time output power of the heater on the sample side.

9. The method for correcting dynamic characteristics of a differential power compensation battery isothermal calorimeter according to claim 7, characterized in that: The heat generation calculation formula in step 10 is: in 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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