Method for measuring specific heat capacity of energy storage battery

Abstract

The invention relates to the technical field of battery thermal performance measurement, in particular to a method for measuring the specific heat capacity of an energy storage battery. The theoretical model is calibrated by monitoring the cooling curve of the battery so as to ensure that the heat transfer characteristic of the battery is accurately reflected. Then, constant-power heating is adopted, so that the thermal field of the battery reaches a quasi-steady state, and in the steady state, the temperature change is gradually consistent; and recording a temperature change curve in real time through a temperature acquisition instrument, and calculating the specific heat capacity of the battery in combination with the calibrated model and a constant power input condition. According to the method, only the voltage-stabilized power supply and the temperature acquisition instrument are needed, so that the cost is greatly reduced; the measurement precision is improved through temperature change curve analysis after model calibration, and the problems that in a traditional method, environmental interference is large, and precision is insufficient are solved; the time for reaching the quasi-steady state is shortened through constant-power heating, and the measurement process is accelerated. The method is suitable for various energy storage batteries, can meet the requirements of industries such as electric automobiles and electric energy storage on the thermal performance of the batteries, and has wide popularization value.

Description

Technical Field

[0001] The invention belongs to the technical field of energy storage batteries, and in particular relates to a method for measuring the specific heat capacity of an energy storage battery. Background Art

[0002] Understanding the specific heat capacity of energy storage batteries is of great significance for controlling their thermal performance. The specific heat capacity of energy storage batteries indicates the ability of batteries to handle heat, and some experts and scholars have recently conducted research on it.

[0003] The invention patent with application publication number CN 108732204A discloses a method and device for measuring the specific heat capacity of a power battery. This method takes a square hard-shell lithium iron phosphate battery as the research object and measures its specific heat capacity by inputting a certain amount of heat into the battery. Unlike the method described in which the specific heat capacity of the battery is calculated using data after the battery thermal field reaches a "quasi-steady state", this method uses data after the battery heating is completed to calculate the specific heat capacity of the battery, which belongs to the "steady state" method test category and has a longer test time.

[0004] Chinese patent 201410847949.5 discloses a method for determining the specific heat capacity of a power battery. This method places the battery to be tested in the test chamber of an accelerated adiabatic calorimeter, and then uses a heater to heat the battery. During the test, the accelerating calorimeter automatically compensates the energy of the test chamber according to the temperature change on the surface of the battery, keeping the chamber temperature consistent with the surface temperature of the battery. This test method has a slow temperature balance, a long test cycle and a high test cost. In addition, due to the low thermal conductivity of the battery, the internal and external temperatures will be uneven during the heating process, affecting the test accuracy. Summary of the invention

[0005] Based on the above technical problems, the present invention provides a method for measuring the specific heat capacity of an energy storage battery, aiming to propose a measurement method with low cost and high precision.

[0006] The technical solution adopted by the present invention is:

[0007] S1. The specific heat capacity experimental measurement of the energy storage battery mainly includes:

[0008] S1.1. Theoretical analysis of specific heat capacity test of energy storage batteries:

[0009] (S1.1) Treat the energy storage battery as a homogeneous entity and heat it at a constant power;

[0010] (S1.2) Assume that the mass, specific heat capacity, and temperature of the battery are m, c, and T respectively, and the heating power is P. The battery is continuously heated. When the battery thermal field reaches a quasi-steady state, P = cmdT / dt. From this, the specific heat capacity expression of the energy storage battery can be obtained: c = P / m(dT / dt).

[0011] S1.2. Heat loss calibration:

[0012] (S1.2.1) Keep the battery warm, assuming its initial temperature and ambient temperature are T i ;

[0013] (S1.2.2) Heat the battery to a preset temperature and then allow it to cool down freely; fit the battery temperature drop equation T d (t), and find the first-order derivative dT d / dt (take positive value), that is, the battery temperature drop rate, then cmdT d / dt is the heat loss of the battery;

[0014] S1.3. Experimental test methods:

[0015] (S1.3.1) Adjust the battery temperature and ambient temperature to T i , heat the energy storage battery at constant power and monitor temperature changes;

[0016] (S1.3.2) Calculate the average temperature of the battery, fit its equation with time, and find the first-order inverse to obtain the battery temperature rise rate dT r / dt;

[0017] (S1.3.3) The model shown in step (S1.2) is an expression of the specific heat capacity of the battery derived under ideal conditions. In a real environment, due to the existence of heat loss, the temperature rise rate dT when the battery thermal field reaches a quasi-steady state is r / dt is lower than that in the ideal state. According to the law of conservation of energy, when the temperature difference between the initial temperature and the temperature difference between the battery during the temperature rise and the temperature drop is equal (i.e. ΔT r =ΔT d ), the battery has equal heat loss, then the actual specific heat capacity expression of the energy storage battery is:

[0018] c=P / m(dT r / dt+dT d / dt)| ΔTr＝ΔTd (Formula 1)

[0019] Preferably, the initial battery temperature and the ambient temperature can be provided by an accelerated adiabatic calorimeter, a high and low temperature test chamber or a constant temperature water tank.

[0020] Preferably, the heat-insulating state is created with the aid of heat-insulating materials such as aerogel and pearl cotton.

[0021] Preferably, the constant power heating of the energy storage battery should ensure that the thickness of the heating film is not higher than 0.2 mm, the mass is less than 2% of the total mass of the battery, the heating power is affected by temperature and voltage by less than 1%, and the size of the heating film can completely cover the large surface of the battery.

[0022] Preferably, an infrared thermal imager, a thermocouple or an optical fiber is used to monitor the temperature change at the center of the large surface of the battery.

[0023] Preferably, the heat loss calibration of the energy storage battery has an upper limit temperature of the battery lower than the safe operating temperature of the battery; after the heating is stopped, the battery temperature drops below T i Stop the test at +5℃.

[0024] Preferably, during the specific heat capacity test process of the energy storage battery, the heating time t' of the battery is not less than 120s, so as to ensure that the thermal field of the battery reaches a quasi-steady state.

[0025] Preferably, the batteries targeted by the method of the present invention include but are not limited to square, soft-pack and cylindrical lithium-ion batteries, sodium-ion batteries, etc. for energy storage, and are also applicable to lithium-ion and sodium-ion batteries for power use in various shapes.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] First, low cost: The specific heat capacity of the energy storage battery proposed in the present invention is measured by coating the battery with inexpensive thermal insulation materials such as aerogel and pearl cotton during the experiment, and then heating the battery with an electric heating film. Compared with the use of an accelerated adiabatic calorimeter to test the specific heat capacity of the battery, this method has significant cost advantages.

[0028] High precision: The theoretical model of specific heat capacity of energy storage batteries proposed in the present invention takes into account the influence of heat loss. Compared with the calculation of the specific heat capacity of batteries using an ideal mathematical model, the precision is significantly improved.

[0029] Fast speed: The measurement method proposed in the present invention can measure the specific heat capacity of the battery in about 600 seconds. Compared with the steady-state method for testing the specific heat capacity of the battery with a test cycle of several hours, the test cycle of this method is short and fast.

[0030] Second, the method for measuring specific heat capacity of power lithium-ion batteries of the present invention effectively solves the problems of insufficient accuracy, complex environmental interference and dependence on measuring equipment encountered in the prior art in measuring thermal performance of batteries in industrial applications, and has achieved significant technical progress, as follows:

[0031] 1. Existing technical problems solved

[0032] Insufficient measurement accuracy: Traditional specific heat capacity measurement methods often have large measurement errors due to convection heat dissipation and equipment limitations, and cannot accurately reflect the thermal capacity characteristics of power lithium batteries. This invention uses aerogel felt to wrap the battery and place it in a vacuum environment, which effectively suppresses convection heat loss, improves measurement accuracy, and solves the problem of large errors in traditional methods.

[0033] Environmental interference: It is difficult to completely eliminate the influence of ambient temperature changes on experimental results with existing measurement methods, resulting in unstable measurement data. The present invention controls the initial temperature of the battery in a high and low temperature test chamber and uses a voltage-stabilized power supply to maintain constant power heating, thereby ensuring the stability of temperature input and significantly reducing the interference of the external environment on the experiment.

[0034] The measurement equipment is complex and costly: Traditional methods often require high-precision equipment and complex experimental devices, which results in a cumbersome measurement process, high cost, and difficulty in promotion. The present invention uses a conventional voltage-stabilized power supply, an electric heating film, and a temperature acquisition instrument to achieve accurate specific heat capacity measurement with relatively simple equipment, greatly reducing equipment dependence and measurement costs.

[0035] 2. Significant technological progress

[0036] The measurement process is simplified and the accuracy is improved: Through aerogel vacuum coating and thermocouple temperature monitoring, external interference is eliminated, making the battery specific heat capacity measurement process simpler while ensuring experimental accuracy. This improvement effectively reduces measurement errors, improves the credibility of experimental results, and provides reliable heat capacity data support for thermal management research of power batteries.

[0037] Wide applicability: The present invention is applicable to different sizes and types of power lithium batteries on the market, including soft-pack, cylindrical and other structures, and can meet the needs of different energy storage devices. This wide applicability makes the method more valuable in the field of power battery thermal performance testing, and is conducive to popularization and application in industries such as electric vehicles and power energy storage.

[0038] Improved measurement efficiency and cost-effectiveness: The electric heating film and voltage-stabilized power supply used in this method are low-cost, the experimental equipment is lightweight, easy to operate, and suitable for large-scale promotion and application. Compared with traditional methods, this invention significantly reduces experimental costs and complexity, improves the efficiency and economy of battery thermal capacity testing, and is particularly suitable for industrial application scenarios with high demand for rapid testing.

[0039] Guaranteed experimental safety: By real-time monitoring of battery temperature and limiting the maximum temperature to below 80°C, the present invention reduces the risk of battery overheating during the measurement process and improves experimental safety. This safety design ensures the reliability of battery performance measurement, provides a safe data basis for battery thermal management, and is suitable for industrial testing applications.

[0040] In summary, the method for measuring the specific heat capacity of a power lithium-ion battery of the present invention has achieved significant progress in measurement accuracy, cost-effectiveness, environmental adaptability and experimental safety, solved many shortcomings of traditional methods, and provided a reliable and simple heat capacity measurement solution for the power battery industry. It has wide application value in the fields of electric vehicles, power energy storage and consumer electronics. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a schematic diagram of the two-dimensional structure of the energy storage battery mentioned in the embodiment of the present invention, in which: 1-symmetry plane, 2-thermocouple, 3-battery core, 4-battery shell, 5-large heated surface, 6-electric heating film.

[0042] Figure 2 is a temperature drop curve diagram of the energy storage battery in the heat preservation state during the heat loss calibration process mentioned in the embodiment of the present invention, in which T avg and T i are the average battery temperature and the ambient temperature respectively;

[0043] Figure 3 It is a temperature rise diagram of the energy storage battery mentioned in the embodiment of the present invention when it is heated in a heat preservation state;

[0044] Figure 4 This is a curve chart showing the variation of specific heat capacity of the energy storage battery measured in the embodiment of the present invention with temperature. DETAILED DESCRIPTION

[0045] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0046] This embodiment provides a method for measuring the specific heat capacity of a power lithium-ion battery, which is applicable to energy storage batteries of various sizes on the market.

[0047] The specific heat capacity measurement method of the energy storage battery provided in this embodiment is:

[0048] In this embodiment, the energy storage battery is a soft-pack lithium iron phosphate battery, and the size, mass, and nominal capacity are 11×79×130mm respectively. 3 , 235g, 9.0Ah. The battery is first wrapped with 10mm thick aerogel felt, then placed in a vacuum box with the air pressure adjusted to -90kPa to reduce convective heat loss;

[0049] In this embodiment, two batteries are taken and placed close together, and then electric heating films of suitable size are pasted on the large external surfaces of the two batteries. Then, thermocouples are arranged between the heated surface of the battery and the large surface in close contact. The thermocouples are connected to an external temperature collector to monitor the temperature changes of the batteries, and finally the average temperature of the batteries is obtained. The two-dimensional view of the battery and the arrangement of the thermocouples are shown in the figure. Figure 1 As shown;

[0050] In this embodiment, the ambient temperature and the initial temperature of the battery are provided by a high and low temperature test chamber;

[0051] In this embodiment, the battery state of charge is 50%;

[0052] In this embodiment, the heater is provided with a constant input power through a voltage-regulated power supply;

[0053] In this embodiment, the size of the electric heating film used is the same as the large surface size of the battery, with a thickness of 0.2 mm and a mass of 2.0 g. The heating power is affected by temperature by no more than 1.0%;

[0054] In this embodiment, the battery is regarded as a homogeneous entity and the influence of the tab is not considered;

[0055] In this embodiment, the self-heating of the battery is ignored and the maximum temperature of the battery is limited to less than 80°C;

[0056] The method for measuring the specific heat capacity of a power lithium-ion battery provided in this embodiment obtains the average temperature rise and specific heat capacity of the battery by controlling the experimental environment and accurately monitoring the battery temperature. The specific working principle is as follows:

[0057] 1. Experimental preparation and environment setup

[0058] First, select the target battery (such as the soft-pack lithium iron phosphate battery in this example) and record its size, mass and nominal capacity. In order to reduce the convective heat transfer error in the experiment, the battery is coated with a 10mm thick aerogel felt and placed in a vacuum box with the air pressure adjusted to -90kPa. The vacuum environment can effectively suppress the heat loss caused by air convection, thereby more accurately recording the temperature rise characteristics of the battery itself. In addition, the ambient temperature and the initial temperature of the battery are controlled by a high and low temperature test chamber to ensure the controllability and consistency of the experimental environment.

[0059] 2. Electric heating film installation and thermocouple arrangement

[0060] Next, place the two batteries side by side and stick the electric heating film on the outer large surface of the battery. The size of the electric heating film is the same as the large surface of the battery, with a thickness of 0.2mm and a mass of 2.0g, which can provide uniform and stable heat input. Then, a thermocouple is arranged between the heated surface of the battery and the large surface that is close to it. The thermocouple is connected to a temperature collector to monitor the temperature changes on the surface and inside of the battery in real time, so that the temperature distribution and average temperature rise of the battery during the heating process can be accurately recorded.

[0061] 3. Control heating power and monitor temperature rise

[0062] During the experiment, a constant power input is provided to the electric heating film through a voltage-stabilized power supply to ensure that the battery receives stable heat. The heating power of the electric heating film is affected by temperature by no more than 1.0%, thereby ensuring the stability of the heating power. Since the battery state of charge is maintained at 50%, the self-heating effect of the battery is small in this state, so the self-heating effect of the battery is ignored. For safety and accuracy, the experiment sets the maximum temperature of the battery not to exceed 80°C, and records the temperature change curve of the battery under this condition.

[0063] 4. Specific heat capacity calculation

[0064] After the experiment, the average temperature rise of the battery is calculated based on the battery temperature change curve recorded during the heating process. Since the input power of the electric heating film, the heating time and the mass of the battery are known in the experiment, the specific heat capacity formula \(C=\frac{Q}{m\cdot\Delta T}\) is used for calculation. Among them, \(Q\) is the heat provided by the electric heating film, \(m\) is the mass of the battery, and \(\DeltaT\) is the average temperature rise of the battery. The specific heat capacity of the battery is obtained by this formula, and the thermal performance of the power lithium-ion battery can be accurately measured.

[0065] In this embodiment, the specific heat capacity of the energy storage battery is divided into a theoretical model construction and an experimental test process:

[0066] S1.1. Theoretical analysis of specific heat capacity test of energy storage batteries:

[0067] (S1.1) Treat the energy storage battery as a homogeneous entity and heat it at a constant power;

[0068] (S1.2) Assume that the mass, specific heat capacity, and temperature of the battery are m, c, and T respectively, and the heating power is P. The battery is continuously heated. When the battery thermal field reaches a quasi-steady state, P = cmdT / dt. From this, the specific heat capacity expression of the energy storage battery can be obtained: c = P / m(dT / dt).

[0069] (S1.3.3) The model shown in step (S1.2) is an expression of the specific heat capacity of the battery derived under ideal conditions. In a real environment, due to the existence of heat loss, the temperature rise rate dT when the battery thermal field reaches a quasi-steady state is r / dt is lower than that in the ideal state. According to the law of conservation of energy, when the temperature difference between the initial temperature and the temperature difference between the battery during the temperature rise and the temperature drop is equal (i.e. ΔT r =ΔT d ), the battery has equal heat loss, then the actual specific heat capacity expression of the energy storage battery is:

[0070] c=P / m(dT r / dt+dT d / dt)| ΔTr＝ΔTd (Formula 1)

[0071] S2. The specific heat capacity test of the energy storage battery includes two processes: heat loss calibration and regular test:

[0072] S2.1. The specific heat capacity measurement method of the energy storage battery, the heat loss calibration process is:

[0073] (S2.1.1) Keep the battery warm and adjust the ambient temperature and battery temperature to 0°C;

[0074] (S2.1.2) Turn on the heater and heat the battery to 41°C at a constant power of 20.0W. When the battery temperature drops to 5°C, stop the experiment. The results are as follows: Figure 2 As shown;

[0075] (S2.1.3) Fitting the battery temperature drop equation T d (t) = -8.99 × 10 -12 t 3 +2.40×10 -7 t 2 -3.06×10 -3 t+18.3

[0076] (S2.1.4) For T d (t) Take the first-order derivative and we get dT d / dt=-2.679×10 -11 t 2 +4.8×10 -7 t-3.06×10 -3 , then cmdT d / dt is the battery heat loss.

[0077] S2.2. The specific heat capacity measurement method of the energy storage battery, the test process is:

[0078] (S2.2.1) Adjust the ambient temperature and the initial temperature of the battery to -28°C;

[0079] (S2.2.2) Heat the battery at a constant power of 20.0 W until its maximum temperature is close to -10°C. Figure 3 As shown;

[0080] (S2.2.3) When the battery thermal field reaches a quasi-steady state, calculate the constant temperature rise rate dT of the battery r / dt, the specific heat capacity of the battery can be calculated according to formula (2).

[0081] According to the above test steps, when the test conditions are changed, the battery specific heat capacity at 0℃, 20℃, 40℃ and 60℃ can be measured. The results are as follows: Figure 4 shown.

[0082] The system for measuring the specific heat capacity of energy storage batteries provided by the present invention accurately measures the specific heat capacity of batteries through the synergy of theoretical model establishment, heat loss calibration, constant power heating test and data processing module. The following is the detailed working principle:

[0083] 1. Establishment of theoretical model

[0084] The theoretical model building module of the system first constructs a specific heat capacity model based on the heat transfer characteristics of the energy storage battery and generates the expression required for measurement. This model is based on the assumption of a homogeneous entity of the energy storage battery and models the relationship between the battery heating power and the temperature change, laying a theoretical foundation for subsequent experimental calculations. The formula provided by this module takes into account the assumption of uniform heating inside the battery, making the specific heat capacity calculation expression have a high accuracy in actual measurement.

[0085] 2. Heat loss calibration

[0086] In the actual measurement process, heat loss will affect the accurate determination of specific heat capacity, so the system is equipped with a heat loss calibration module. This module heats the battery to a preset temperature after coating it with insulation material, then stops heating and records the natural cooling curve. By fitting the temperature drop trend, the temperature drop rate of the battery is obtained, and the heat loss of the battery is calculated. This step ensures that the system can correct the error caused by heat dissipation, making the specific heat capacity measurement result closer to reality.

[0087] 3. Constant power heating and temperature rise monitoring

[0088] The test module heats the battery under constant power conditions and controls the uniformity of heating through the heating film. The temperature change curve of the battery is monitored in real time to ensure that the heating power is constant and stable, and the battery temperature rise curve data is transmitted to the data processing module. The thickness of the heating film is controlled below 0.2 mm, and the mass of the heating film does not exceed 2% of the total mass of the battery, thereby reducing the interference of additional heat and ensuring the accuracy of temperature collection.

[0089] 4. Data processing and specific heat capacity calculation

[0090] After receiving the temperature data of temperature rise and temperature drop, the data processing module calculates the specific heat capacity of the battery according to the principle of energy conservation. By bringing the temperature rise rate, heat loss rate and heating power into the theoretical model, the system obtains the actual specific heat capacity of the battery. Finally, the data processing module outputs the measurement results and provides accurate battery specific heat capacity data to meet the application requirements of energy storage batteries in different temperature control and energy management systems.

[0091] The above embodiment illustrates a method for measuring the specific heat capacity of an energy storage battery provided by the present invention. The above description only explains the technical principle of the present invention and does not limit the protection scope of the present invention. Any modification or replacement made within the scope of the rights of the present invention belongs to the protection scope of the present invention.

Claims

1. A method for measuring the specific heat capacity of an energy storage battery, characterized in that: The specific heat capacity of the battery is measured by establishing a theoretical model and designing experimental conditions, including the following steps: S1.1 Theoretical analysis of specific heat capacity test of energy storage battery: The battery is regarded as a homogeneous entity, heated at a constant power, and the mass, specific heat capacity and temperature of the battery, as well as the power applied to the battery, are set. When the thermal field of the battery reaches a quasi-steady state, the calculation expression of the specific heat capacity is obtained based on these parameters. S1.2 Heat loss calibration: The battery is kept warm and heated to a preset temperature, then cooled naturally. The temperature drop curve is fitted to calculate the temperature drop rate of the battery, and then the heat loss of the battery is calculated. S1.3 Experimental test method: Heat the battery at a constant power, monitor the temperature change and calculate the temperature rise rate. Based on the law of conservation of energy, when the temperature difference between the temperature rise and the temperature drop is equal, use the actual specific heat capacity expression to obtain the specific heat capacity of the battery.

2. The method for measuring specific heat capacity of an energy storage battery according to claim 1, characterized in that: The initial temperature and ambient temperature of the battery are provided by an accelerated adiabatic calorimeter, a high and low temperature test chamber or a constant temperature water bath.

3. The method for measuring specific heat capacity of an energy storage battery according to claim 1, characterized in that: The thermal insulation state of the battery is achieved with the assistance of aerogel or pearl cotton insulation materials.

4. The method for measuring specific heat capacity of an energy storage battery according to claim 1, characterized in that: The thickness of the heating film used for constant power heating of energy storage batteries is no more than 0.2 mm, and its mass does not exceed 2% of the total mass of the battery. The heating power is affected by temperature and voltage by less than 1%, and the size of the heating film can cover a large surface of the battery.

5. The method for measuring specific heat capacity of an energy storage battery according to claim 1, characterized in that: Use infrared thermal imagers, thermocouples or fiber optic temperature sensors to monitor the temperature changes in the center of the large surface of the battery.

6. The method for measuring specific heat capacity of an energy storage battery according to claim 1, characterized in that: Suitable for square, soft-pack, cylindrical energy storage lithium-ion batteries, sodium-ion batteries and power lithium-ion batteries, sodium-ion batteries.

7. A system for measuring specific heat capacity of energy storage batteries, characterized in that: Includes the following modules: Theoretical model building module, used to build a theoretical model of specific heat capacity based on the heat transfer characteristics of the energy storage battery and provide the formula required for measurement; Heat loss calibration module, used to heat the battery to a preset temperature under insulation state and monitor the natural cooling process, fit the temperature drop curve and calculate the heat loss of the battery; The test module is used to monitor the temperature rise curve of the battery in real time under constant power heating conditions, calculate the temperature rise rate and calculate the specific heat capacity in combination with the theoretical model; The data processing module is used to calculate the battery specific heat capacity and output the measurement results based on the principle of energy conservation.

8. The energy storage battery specific heat capacity measurement system according to claim 7, characterized in that: It also includes a temperature control module for adjusting the initial temperature of the battery and the environment. The temperature control module is composed of an accelerated adiabatic calorimeter, a high and low temperature test chamber or a constant temperature water tank.

9. The energy storage battery specific heat capacity measurement system according to claim 7, characterized in that: It also includes a heat preservation auxiliary module, which is made of aerogel or pearl cotton material and is used to reduce heat loss during battery measurement.

10. The energy storage battery specific heat capacity measurement system according to claim 7, characterized in that: The test module includes a constant power heating device, the heating film thickness of the heating device is not higher than 0.2 mm, the mass does not exceed 2% of the total mass of the battery, and the size can cover the large surface of the battery. The heating power is affected by temperature and voltage to less than 1%.

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