Method for measuring instantaneous heat production power of lithium battery

Abstract

The invention discloses a lithium battery instantaneous heat production power measurement method, which comprises the following steps of: spraying blackbody paint on the surface of a lithium battery sample, and placing the lithium battery sample on a heat insulation bracket of a constant-temperature box; the lithium battery sample is connected with a charging and discharging device, and surface temperature change in the heat production process of the lithium battery sample and surface temperature drop data after charging and discharging are measured through a thermal infrared imager; calculating an equivalent surface heat exchange coefficient of the lithium battery sample according to the surface temperature drop data of the lithium battery sample; and establishing a thermal simulation model according to the thermophysical parameters of the lithium battery, and dynamically optimizing the heating power data according to the goodness of fit between the simulation temperature change and the actually measured temperature change to obtain the instantaneous heat production power data of the lithium battery sample. According to the method, the infrared non-contact temperature measurement technology is used for recording the surface temperature rise data of the lithium battery in the charging and discharging states, the thermal simulation model is established according to the thermophysical parameters, the instantaneous heat production power of the lithium battery is calculated by using the dynamic parameter optimization algorithm, the calculation process is rapid, and the test precision is high.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a method for measuring the instantaneous heat generation power of a lithium battery. Background Art

[0002] The heat generation power of lithium batteries during charging and discharging is a key indicator of thermal safety and thermal management of lithium batteries, and is an important parameter to guide the design and development of lithium batteries. Due to certain structural differences in lithium batteries and their large specific heat capacity, it is difficult to accurately measure the instantaneous heat generation power of lithium batteries. When the traditional adiabatic or isothermal method is used to measure the heat generation power of lithium batteries, the conduction and accumulation of heat will affect the test results, causing deviations in the test results. Temperature sensors such as thermocouples themselves will also affect the test of heat generation power.

[0003] Under the natural convection boundary of air, the heat generated by lithium batteries during the charging and discharging process not only increases the temperature of the lithium batteries themselves, but also some heat is dissipated into the air. According to the law of conservation of energy, it can be written as:

[0004] Q=mcΔT(t)+hsΔT(t)

[0005] Where T(t) is the temperature rise of the sample over time. When the boundary condition is adiabatic, the formula can be simplified to:

[0006] Q=mcΔT(t)

[0007] The above is the basic principle of the adiabatic measurement method. In actual situations, due to the anisotropic thermal parameters and structure of lithium batteries, the surface temperature rise T(t) measured by traditional methods cannot represent the average temperature rise of the sample. Moreover, when calculating the heat generation power, due to the hysteresis effect, it is often difficult to calculate the accurate instantaneous heat generation power from the heat generation. Summary of the invention

[0008] The present invention proposes a method for measuring the instantaneous heat generation power of a lithium battery based on dynamic parameter optimization to solve the above technical problems. A thermal model is established using the thermal parameters of the lithium battery, and the surface temperature change is used as the optimization target parameter to accurately calculate the instantaneous heat generation power of the lithium battery.

[0009] In order to achieve the above object, the technical solution adopted by the present invention is:

[0010] A method for measuring the instantaneous heat generation power of a lithium battery comprises the following steps:

[0011] Step S101, after spraying black body paint on the surface of the lithium battery sample, place it on an insulating bracket of a constant temperature box;

[0012] Step S102, the lithium battery sample is connected to a charging and discharging device, and the temperature of the lithium battery sample is uniform with the ambient temperature as the starting temperature, and the surface temperature change of the lithium battery sample during heat generation is measured by an infrared thermal imager;

[0013] Step S103, after the charge and discharge process is completed, the infrared thermal imager continues to measure the surface temperature drop data of the lithium battery sample;

[0014] Step S104, calculating the equivalent surface heat transfer coefficient of the lithium battery sample according to the surface temperature drop data of the lithium battery sample;

[0015] Step S105, establishing a thermal simulation model according to the thermal physical property parameters of the lithium battery, dynamically optimizing the heating power data according to the degree of agreement between the simulated temperature change and the measured temperature change, and obtaining the instantaneous heat generation power data of the lithium battery sample.

[0016] Preferably, in step S104, "calculating the equivalent surface heat transfer coefficient of the lithium battery sample according to the surface temperature drop data of the lithium battery sample" is specifically:

[0017] The lithium battery sample enters a quasi-steady state of cooling. Based on the temperature drop curve and the specific heat capacity data of the lithium battery sample, the equivalent surface heat transfer coefficient h of the lithium battery sample is calculated by the following formula:

[0018] hsΔT(t)=mcΔT(t),

[0019] Among them, ΔT(t) is the temperature change curve in the cooling stage, c is the specific heat capacity of the lithium battery sample, h is the equivalent surface heat transfer coefficient, s is the surface area of ​​the lithium battery sample, and m is the mass of the lithium battery sample.

[0020] As a preference, Figure 2 As shown, step S105 includes the following steps:

[0021] Step S1051, establishing a thermal simulation model in combination with the thermal physical property parameters of the lithium battery, and setting initial heating power data that changes with time;

[0022] Step S1052, dynamically optimizing heating power data according to the degree of agreement between the simulated temperature change and the measured temperature change;

[0023] Step S1053, when the simulated temperature change curve meets the set error index, the heating power obtained is the instantaneous heat generation power data of the lithium battery sample.

[0024] Preferably, in step S1052, the heat generation process of the lithium battery sample is divided into a plurality of time periods, and the heating power data are dynamically optimized for the plurality of time periods in chronological order.

[0025] Compared with the prior art, the present invention can calculate the instantaneous heat generation power of lithium batteries using a relatively simple experimental device. The hardware system is simple, the calculation process is fast, and the test accuracy is high, which greatly improves the test efficiency and reduces the test cost. Compared with the traditional heat generation test method, the present invention uses a non-contact measurement method to simplify the sample processing process, and uses the method of establishing a thermal model and dynamic parameter optimization to take into account the influencing factors such as the internal temperature distribution and surface heat loss of the sample, so that accurate lithium battery instantaneous heat generation power data can be quickly obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A schematic diagram of a flow chart of a method for measuring instantaneous heat generation power of a lithium battery according to the present invention;

[0027] Figure 2 This is a flow chart of step S105 of a method for measuring instantaneous heat generation power of a lithium battery according to the present invention;

[0028] Figure 3 The figure is a schematic diagram of the hardware system structure used in a method for measuring the instantaneous heat generation power of a lithium battery according to the present invention.

[0029] Figure 4 A comparison chart of preset simulated power and dynamically optimized instantaneous power of the lithium battery sample of Example 1;

[0030] Figure 5 A comparison chart of preset simulated power and dynamically optimized instantaneous power of the lithium battery sample of Example 2;

[0031] Figure 6 FIG. 1 is a schematic diagram of instantaneous power during discharge of a lithium battery sample according to an embodiment of the present invention.

[0032] In the picture, 1-infrared thermal imager, 2-lithium battery sample, 3-charging and discharging connecting wires. DETAILED DESCRIPTION

[0033] The present invention will be described in detail below in conjunction with the specific embodiments shown in the accompanying drawings. However, these embodiments do not limit the present invention, and any structural, methodological, or functional changes made by a person skilled in the art based on these embodiments are all within the scope of protection of the present invention.

[0034] The terms used in the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The singular forms "a", "the" and "the" used in the present invention and the appended claims are also intended to include plural forms unless the context clearly indicates other meanings. It should also be understood that the term "and / or" used herein refers to and includes any or all possible combinations of one or more associated listed items.

[0035] like Figure 1 As shown, a method for measuring the instantaneous heat generation power of a lithium battery comprises the following steps:

[0036] Step S101, after the surface of the lithium battery sample is sprayed with black paint, it is placed on an insulating support of a constant temperature box.

[0037] The lithium battery sample 2 is placed on an insulating bracket in a constant temperature box so that each surface of the lithium battery is in a state of natural air convection; the surface of the lithium battery sample 2 is sprayed with black body paint to facilitate temperature measurement by the infrared thermal imager 1.

[0038] Step S102, the lithium battery sample is connected to the charging and discharging device, the temperature of the lithium battery sample is uniform with the ambient temperature as the starting temperature, and the surface temperature change of the lithium battery sample during the heat generation process is measured by an infrared thermal imager.

[0039] like Figure 2 As shown, the hardware system used in the present invention is composed of a lithium battery sample 2, an infrared thermal imager 1 and a charging and discharging device. The lithium battery sample 2 is connected to the charging and discharging device through a charging and discharging connecting line 3 to start charging and discharging, and the infrared thermal imager 1 is used to record the surface temperature changes of the lithium battery sample 2 during the heat generation process.

[0040] Step S103: After the charge and discharge process is completed, the infrared thermal imager continues to measure the surface temperature drop data of the lithium battery sample. The surface temperature drop data of the lithium battery sample is used to calculate the equivalent surface heat transfer coefficient of the lithium battery sample.

[0041] Step S104, calculating the equivalent surface heat transfer coefficient of the lithium battery sample according to the surface temperature drop data of the lithium battery sample.

[0042] During the charging and discharging process, there is a certain amount of heat exchange between the lithium battery sample and the air. This heat exchange can be regarded as an ideal first-class boundary condition. The equivalent heat transfer coefficient between the air and the lithium battery sample is h. The equivalent heat transfer coefficient h directly affects the surface temperature change of the lithium battery, and its numerical value needs to be clearly defined. In order to obtain the equivalent heat transfer coefficient h, after the charging and discharging process is completed, continue to record the surface temperature drop data of the lithium battery sample. After a certain period of time, the lithium battery sample enters a quasi-steady state of cooling. According to the temperature drop curve combined with the specific heat capacity data of the lithium battery sample, the equivalent surface heat transfer coefficient h of the lithium battery sample is calculated by the following formula:

[0043] hsΔT(t)=mcΔT(t),

[0044] Among them, ΔT(t) is the temperature change curve in the cooling stage, c is the specific heat capacity of the lithium battery sample, h is the equivalent surface heat transfer coefficient, s is the surface area of ​​the lithium battery sample, and m is the mass of the lithium battery sample.

[0045] Step S105, establishing a thermal simulation model according to the thermal physical property parameters of the lithium battery, dynamically optimizing the heating power data according to the degree of agreement between the simulated temperature change and the measured temperature change, and obtaining the instantaneous heat generation power data of the lithium battery sample.

[0046] Specifically, step S105 includes the following steps:

[0047] Step S1051, establishing a thermal simulation model in combination with the thermal physical property parameters of the lithium battery, and setting initial heating power data that changes with time.

[0048] Based on the above measurements, combined with the anisotropic thermal conductivity and other thermal physical parameters of the lithium battery sample, an equivalent thermal simulation model of the thermal behavior of the lithium battery is established. The initial heating power data that changes with time is the preset simulation power.

[0049] Step S1052, dynamically optimizing the heating power data according to the degree of agreement between the simulated temperature change and the measured temperature change.

[0050] Set the initial heating power that changes with time for the model, compare the simulated surface temperature change with the measured temperature change, and if the simulated temperature is too low or too high, dynamically adjust the corresponding heating power to increase or decrease.

[0051] In actual situations, the charge and discharge time of lithium batteries is often 1000s (3C), 3600s (1C) or even longer. The heat generation and temperature rise in the previous time period during the charge and discharge time may have a significant impact on the temperature rise data in the next time period. In order to improve the accuracy of dynamic parameter optimization and speed up the model simulation efficiency, the heat generation process of lithium battery samples can be divided into multiple time periods, and the heating power data of the multiple time periods can be dynamically optimized in chronological order.

[0052] Step S1053, when the simulated temperature change curve meets the set error index, the heating power obtained is the instantaneous heat generation power data of the lithium battery sample.

[0053] The dynamic parameters of the heating power are optimized and updated cyclically until the simulated temperature and the measured temperature meet the set error index, thereby obtaining the optimal instantaneous heat generation power data result, which is the instantaneous heat generation power data of the lithium battery sample. The set error index is preset after multiple tests.

[0054] After a single test, the initial temperature of the sample can be changed to conduct a thermal property test at the next temperature point, and the instantaneous heat generation power of the sample at different temperatures can be continuously measured. Figure 4 and Figure 5 The figures are respectively a comparison diagram of the preset simulation power and the dynamically optimized instantaneous power of the lithium battery samples of the first embodiment and the second embodiment, Figure 6FIG. 1 is a schematic diagram of instantaneous power during discharge of a lithium battery sample according to an embodiment of the present invention.

[0055] The present invention measures the surface temperature change of the sample under the heat generation state through infrared non-contact temperature measurement technology, establishes a thermal simulation model in combination with the thermal physical properties of the sample, takes the temperature matching degree as the optimization goal, and performs dynamic parameter optimization of the heating power to obtain the instantaneous heat generation power of the sample.

[0056] Those skilled in the art will readily appreciate other embodiments of the present invention after considering the specification and practicing the invention disclosed herein. This application is intended to cover any variations, uses or adaptations of the present invention, which follow the general principles of the present invention and include common knowledge or customary techniques in the art that are not disclosed by the present invention. The specification and examples are intended to be exemplary only, and the true scope and spirit of the present invention are indicated by the claims of the present application.

[0057] It should be understood that the present invention is not limited to the exact construction that has been described above and shown in the drawings and that various modifications and changes may be made without departing from the scope thereof. The scope of the present invention is limited only by the appended claims.

Claims

1. A method for measuring the instantaneous heat generation power of a lithium battery, characterized in that: The steps include: Step S101, after spraying black body paint on the surface of the lithium battery sample, place it on an insulating bracket of a constant temperature box; Step S102, the lithium battery sample is connected to a charging and discharging device, and the temperature of the lithium battery sample is uniform with the ambient temperature as the starting temperature, and the surface temperature change of the lithium battery sample during heat generation is measured by an infrared thermal imager; Step S103, after the charge and discharge process is completed, the infrared thermal imager continues to measure the surface temperature drop data of the lithium battery sample; Step S104, calculating the equivalent surface heat transfer coefficient of the lithium battery sample according to the surface temperature drop data of the lithium battery sample; Step S105, establishing a thermal simulation model according to the thermal physical property parameters of the lithium battery, dynamically optimizing the heating power data according to the degree of agreement between the simulated temperature change and the measured temperature change, and obtaining the instantaneous heat generation power data of the lithium battery sample.

2. A method for measuring instantaneous heat generation power of a lithium battery according to claim 1, characterized in that: In the step S104, "calculating the equivalent surface heat transfer coefficient of the lithium battery sample according to the surface temperature drop data of the lithium battery sample" is specifically: The lithium battery sample enters a quasi-steady state of cooling. Based on the temperature drop curve and the specific heat capacity data of the lithium battery sample, the equivalent surface heat transfer coefficient h of the lithium battery sample is calculated by the following formula: hsΔT(t)=mcΔT(t), Among them, ΔT(t) is the temperature change curve in the cooling stage, c is the specific heat capacity of the lithium battery sample, h is the equivalent surface heat transfer coefficient, s is the surface area of ​​the lithium battery sample, and m is the mass of the lithium battery sample.

3. A method for measuring instantaneous heat generation power of a lithium battery according to claim 1, characterized in that: The step S105 includes the following steps: Step S1051, establishing a thermal simulation model in combination with the thermal physical property parameters of the lithium battery, and setting initial heating power data that changes with time; Step S1052, dynamically optimizing heating power data according to the degree of agreement between the simulated temperature change and the measured temperature change; Step S1053, when the simulated temperature change curve meets the set error index, the heating power obtained is the instantaneous heat generation power data of the lithium battery sample.

4. A method for measuring instantaneous heat generation power of a lithium battery according to claim 3, characterized in that: In the step S1052, the heat generation process of the lithium battery sample is divided into a plurality of time periods, and the heating power data of the plurality of time periods are dynamically optimized in chronological order.

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