A fast and low-cost method for measuring the heat generated by charging and discharging of lithium-ion batteries

Abstract

The application provides a kind of fast low-cost lithium ion battery charge-discharge heat generation measurement method, to solve the problems such as complex equipment, high cost, cumbersome operation in the prior art measurement method.The method comprises the following steps: completely immerse the measured lithium ion battery in liquid medium, ensure uniform temperature by stirring, record initial temperature;Apply charge-discharge condition to the battery, record the termination temperature;Based on the volume and specific heat capacity of the liquid medium, calculate the heat generation and heat generation power of the battery;By using the standard sample for correction, further correct the heat generation measurement value, and finally obtain the real heat generation and heat generation power of the battery.The application simplifies the operation process, has the advantages of simple operation, low cost and easy popularization, and is suitable for the test and heat generation analysis of lithium ion battery, and has wide application prospect and popularization value in the field of battery test.

Description

TECHNICAL FIELD

[0001] The application provides a fast and low-cost lithium ion battery charge-discharge heat generation measurement method, and belongs to the technical field of battery testing. BACKGROUND

[0002] As a high-efficiency energy storage device, lithium ion batteries are widely used in electronic devices, vehicles and energy storage systems. With the increasing demand for lithium ion batteries in high-power applications, the heat generation problem of the battery during charging and discharging becomes particularly important and directly affects the design of the battery thermal management system. Excessive battery temperature not only accelerates its aging and shortens its service life, but also may cause safety hazards; while too low temperature will affect the performance of the battery. Therefore, accurately measuring the heat generation and heat generation power of lithium ion batteries during charging and discharging is of great significance for optimizing the battery thermal management system. At present, although methods such as adiabatic accelerating calorimetry and isothermal calorimetry can provide high-precision results, they rely on complex test equipment and longer test time, resulting in high test cost; while simple measurement methods, such as calculating heat generation and heat generation power through battery surface temperature, do not fully consider the influence of environmental factors (such as the temperature uniformity of the heat-absorbing medium) and the shape of the battery, which may lead to large measurement errors. Therefore, developing a fast, low-cost and widely promoted battery heat generation measurement method has become an urgent need in the current technical field. SUMMARY

[0003] The application provides a fast and low-cost lithium ion battery charge-discharge heat generation measurement method, which aims to solve the problems of complex equipment, high cost and difficulty in popularization in the prior art. Through optimization of the measurement method, the application avoids the dependence of traditional accurate measurement methods on harsh test conditions, greatly reduces the test cost, and significantly improves the test efficiency.

[0004] A fast and low-cost lithium ion battery charge-discharge heat generation measurement method, specifically comprising the following steps:

[0005] Step 1: completely immerse the measured lithium ion battery in a liquid medium, ensure that the battery and the liquid medium have the same temperature by stirring, record the temperature of the liquid medium at this time as the initial temperature, and record the volume of the liquid medium at the same time.

[0006] Step 2: apply a charge-discharge working condition to the measured lithium ion battery, and keep the temperature of the liquid medium uniform by stirring. During the charging and discharging process, the battery temperature is measured and recorded in real time until the charging and discharging working condition is completed and the battery and the liquid medium have the same temperature. Record the temperature of the liquid medium at this time as the termination temperature.

[0007] Third step: Calculate the heat generation measurement of the battery using formula (1) according to the volume and volumetric specific heat capacity of the liquid medium in the first step, and the temperature data obtained in step 2:

[0008] Q measured = c V V(T end -T start ), (1)

[0009] Where Q measured is the heat generation measurement of the battery, c V is the volumetric specific heat capacity of the liquid medium, V is the volume of the liquid medium, T end and T start are the final and initial temperatures of the liquid medium, respectively. Calculate the heat generation power measurement of the battery using formula (2):

[0010]

[0011] Where q measured (t) is the heat generation power measurement of the battery, and T(t) is the real-time temperature of the liquid medium.

[0012] Fourth step: Use the heat generation standard sample to measure and calculate the heat generation correction value of the battery under the same test conditions.

[0013] First, replace the measured lithium-ion battery with a standard sample of the same shape and controllable heat generation power, place it in the same initial temperature and the same volume of the same liquid medium, and ensure that the standard sample and the liquid medium have the same temperature through the same stirring rate;

[0014] Next, control the standard sample to release heat according to the heat power calculated by formula (3) until it reaches the time length of the charging and discharging conditions of the measured battery:

[0015]

[0016] Where q standard is the heat power of the standard sample, t is the time, I and R are the charging and discharging current and internal resistance of the measured battery, respectively, T is the temperature of the measured battery (given by the second step), and E eq is the equilibrium electromotive force of the measured battery;

[0017] Then, during the heat release process of the standard sample, keep the temperature of the liquid medium uniform by stirring until the heat release of the standard sample ends and the temperature of the standard sample and the liquid medium is the same, measure and record the temperature of the liquid medium at this time as the final temperature;

[0018] Finally, calculate the heat generation correction value according to formula (4):

[0019]

[0020] wherein Q adjusted is the heat generation correction value, τ is the length of time of the charge and discharge working condition of the measured battery, T standard,end is the end temperature of the liquid medium in the correction test, and the remaining symbols have the same meanings as above. The heat generation correction value is calculated according to formula (5):

[0021]

[0022] wherein q adjusted (t) is the heat generation correction value, T standard (t) is the real-time temperature of the liquid medium during the correction test.

[0023] Fifth step: according to the battery heat generation measurement value calculated in the third step and the battery heat generation correction value calculated in the fourth step, the true value of the heat generation of the measured lithium ion battery is calculated according to formula (6):

[0024] Q real = Q measured + Q adjusted , (6)

[0025] wherein Q real is the true value of the heat generation of the measured lithium ion battery. The true value of the heat generation of the measured lithium ion battery is calculated according to formula (6):

[0026] q real (t) = q measured (t) + q adjusted (t), (7)

[0027] wherein q real (t) is the true value of the heat generation of the measured lithium ion battery. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is the step flow chart of the lithium ion battery charge and discharge heat generation measurement method in the embodiment of the present application.

[0029] Figure 2 is the schematic diagram of the lithium ion battery charge and discharge heat generation measurement device in the embodiment of the present application.

[0030] Figure 3 is the lithium ion battery charge and discharge working condition curve in the embodiment of the present application.

[0031] Figure 4 is the schematic diagram of the liquid medium temperature measurement result in the embodiment of the present application.

[0032] Figure 5 is the standard sample heat generation power curve in the embodiment of the present application.

[0033] Figure 6 A corrected lithium-ion battery heat generation power curve for an embodiment of the present application. DETAILED DESCRIPTION

[0034] The fast and low-cost lithium-ion battery charge-discharge heat generation measurement method proposed by the present application is further described below in conjunction with the accompanying drawings and specific implementation cases.

[0035] As shown in Figure 1 , the fast and low-cost lithium-ion battery charge-discharge heat generation measurement method includes the following steps:

[0036] S1. In this embodiment, a lithium-ion battery charge-discharge heat generation measurement device as shown in Figure 2 is built. The measured lithium-ion battery is a 18650 type lithium iron phosphate battery with a rated capacity of 1.1 Ah and a voltage range of 2.5-3.6 V. The battery is completely immersed in a liquid medium. The liquid medium used is silicone oil with a volume of 0.5 L and a volumetric heat capacity of 1.455 kJ / (L·℃). The device inner cavity is a cylinder with a radius of 30 mm and a height of 200 mm, with a clamp in the center for fixing the 18650 type battery. The stirring equipment is stirred at a speed of 300 rpm to ensure uniform distribution of the liquid medium temperature. Finally, the battery surface temperature and the liquid medium temperature are both 25.1℃, and are taken as the initial temperature.

[0037] S2. The measured lithium-ion battery is subjected to the charge-discharge working condition as shown in Figure 3 , and the stirring equipment continues to run at a speed of 300 rpm to maintain the uniform temperature of the liquid medium. During the complete charge-discharge process, the temperature of the battery is measured and recorded in real time until the end of the charge-discharge working condition and the temperature of the battery and the liquid medium is the same, as shown in Figure 4 . At this time, the temperature of the liquid medium is 30.8℃, and is taken as the termination temperature.

[0038] S3. According to the recorded liquid medium volume, volumetric heat capacity, and the initial temperature and termination temperature data obtained in step S2, the battery heat generation measurement value is calculated according to formula (1):

[0039] Q measured = 1.455 kJ / (L·℃) x 0.5 L x (30.8℃-25.1℃) = 4.15 kJ. (8)

[0040] S4. To correct the heat generation measurement value, a standard sample with the same shape as the measured battery and controllable heat generation power is used to replace the measured battery, and the correction measurement is performed in the device as shown in Figure 2 .

[0041] S41. The standard sample is immersed in a liquid medium of silicone oil with a volume of 0.5 L and an initial temperature of 25.1 °C, and stirred by a stirring device at a speed of 300 rpm to ensure that the temperature of the standard sample is consistent with that of the liquid medium.

[0042] S42. The heat power of the standard sample calculated according to formula (3) is controlled to release heat until the length of time when the battery under test is in the charge-discharge working condition, as shown in formula (4). Figure 5

[0043] S43. During the heat release process of the standard sample, the stirring device keeps the temperature of the liquid medium uniform at a speed of 300 rpm until the heat release of the standard sample ends and the temperature of the standard sample is the same as that of the liquid medium. At this time, the temperature of the liquid medium is 30.2 °C, which is recorded as the final temperature.

[0044] S44. The corrected value of the heat production of the standard sample is calculated according to formula (4):

[0045] Q adjusted = 3.76 kJ - 1.455 kJ / (L·℃) x 0.5 L x (30.2 °C - 25.1 °C) = 0.05 kJ. (9)

[0046] S5. According to the measured value of the heat production of the battery calculated in step S3 and the corrected value of the heat production calculated in step S4, the true value of the heat production of the lithium ion battery under test is calculated according to formula (6):

[0047] Q real = 4.15 kJ + 0.05 kJ = 4.20 kJ. (10)

[0048] The true value of the heat production of the lithium ion battery under test is calculated according to formula (7), as shown in formula (8). Figure 6 ​​

Claims

1. A fast and low-cost method for measuring the heat generation of lithium-ion battery charging and discharging, characterized in that, The method comprises the following steps: Step 1: completely immerse the lithium ion battery to be measured in a liquid medium, ensure that the battery and the liquid medium have the same temperature by stirring, record the temperature of the liquid medium at this time as the initial temperature, and record the volume of the liquid medium at the same time; Step 2: apply a charge-discharge working condition to the lithium ion battery to be measured, and keep the temperature of the liquid medium uniform by stirring during the charge-discharge process, measure and record the battery temperature in real time until the end of the charge-discharge working condition and the battery and the liquid medium have the same temperature, and record the temperature of the liquid medium at this time as the termination temperature; Step 3: according to the volume and volumetric heat capacity of the liquid medium in step 1 and the temperature data obtained in step 2, calculate the heat generation measurement value of the battery using formula (1) and the heat generation power measurement value of the battery using formula (2): Q measured = c V V(T end -T start ), (1) wherein Q measured is a heat production measurement of the battery, c V is the volumetric heat capacity of the liquid medium, V is the volume of the liquid medium, T end and T start are the final and initial temperatures of the liquid medium, respectively, q measured (t) is a heat production power measurement of the battery, and T(t) is the real-time temperature of the liquid medium. Step 4: use a standard sample with the same shape as the lithium ion battery to be measured and controllable heat generation power to replace the battery in steps 1 and 2, measure under the same liquid medium and initial temperature conditions, and calculate the heat generation correction value of the battery; Step 5: according to the battery heat generation measurement value calculated in step 3 and the battery heat generation correction value calculated in step 4, obtain the true value of the heat generation of the lithium ion battery to be measured.

2. The method of claim 1, wherein the method is a fast and low cost method for measuring the heat generation of a lithium-ion battery during charging and discharging. The "liquid medium" in step 1 is a liquid medium with good thermal conductivity and no chemical reaction with lithium ion battery materials to ensure the accuracy and safety of the measurement.

3. The method of claim 1, wherein the method is a fast and low cost method for measuring the heat generation of a lithium-ion battery during charging and discharging. The "stirring rate" in step 2 is adjusted according to the volume and viscosity of the liquid medium to ensure the uniformity of the temperature distribution in the liquid medium during the entire charge-discharge process to reduce measurement errors caused by temperature differences in the medium.

4. The method of claim 1, wherein the method is a fast and low cost method for measuring the heat generation of a lithium-ion battery during charging and discharging. The "use a standard sample with the same shape as the lithium ion battery to be measured and controllable heat generation power to replace the battery in steps 1 and 2, measure under the same liquid medium and initial temperature conditions, and calculate the heat generation correction value of the battery" in step 4 comprises the following steps: Step 41: use a standard sample with the same shape and controllable heat generation power to replace the lithium ion battery to be measured, place it in the same initial temperature and the same volume of the same liquid medium, and ensure that the standard sample and the liquid medium have the same temperature by the same stirring rate; Step 42: control the standard sample to release heat according to the heat power calculated by formula (3) until the time length of the charge-discharge working condition of the battery to be measured is reached: where q standard is the heat power of the standard, t is time, I and R are the charge and discharge current and internal resistance of the battery under test, T is the temperature of the battery under test given in step 2, E eq is the equilibrium electromotive force of the battery under test; Step 43: keep the temperature of the liquid medium uniform by stirring during the heat release process of the standard sample until the heat release of the standard sample ends and the standard sample and the liquid medium have the same temperature, measure and record the temperature of the liquid medium at this time as the termination temperature; Step 44: calculate the heat generation correction value according to formula (4) and the heat generation power correction value according to formula (5): where Q adjusted is the heat generation correction value, τ is the length of the charge-discharge working condition of the measured battery, T standard,end is the terminal temperature of the thermal medium in the correction test, q adjusted (t) is the heat generation power correction value, T standard (t) is the real-time temperature of the liquid medium during the correction test, and the remaining symbols have the same meanings as described above.

5. The method of claim 1, wherein the method is a fast and low cost method for measuring the heat generation of a lithium-ion battery during charging and discharging. The "according to the battery heat generation measurement value calculated in step 3 and the battery heat generation correction value calculated in step 4, obtain the true value of the heat generation of the lithium ion battery to be measured" in step 5 comprises the following contents: According to the battery heat generation measurement value calculated in step 3 and the battery heat generation correction value calculated in step 4, calculate the true value of the heat generation of the lithium ion battery to be measured according to formula (6) and the true value of the heat generation power of the lithium ion battery to be measured according to formula (7): Q real = Q measured + Q adjusted , (6) q real (t) = q measured (t) + q adjusted (t), (7) wherein Q real is the true value of the heat generation of the lithium-ion battery under test, q real (t) is the true value of the heat generation power of the lithium-ion battery under test.

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