Rapid low-cost lithium ion battery charging and discharging heat production measurement method

Abstract

The invention provides a rapid and low-cost lithium ion battery charging and discharging heat production measurement method, and aims to solve the problems of complex equipment, high cost, tedious operation and the like in the existing measurement method. The method comprises the following steps: completely immersing a detected lithium ion battery in a liquid medium, stirring to ensure the temperature to be uniform, and recording the initial temperature; applying charging and discharging conditions to the battery, and recording a final temperature; based on the volume and the specific heat capacity of the liquid medium, the heat production quantity and the heat production power of the battery are calculated; and correction is carried out by using a standard sample, the heat production measurement value is further corrected, and finally the real heat production amount and the heat production power of the battery are obtained. The method simplifies the operation process, has the advantages of simplicity and convenience in operation, low cost and easiness in popularization, is suitable for testing and heat production analysis of the lithium ion battery, and has wide application prospect and popularization value in the field of battery testing.

Description

Technical Field

[0001] The invention provides a fast and low-cost lithium-ion battery charging and discharging heat generation measurement method, belonging to the technical field of battery testing. Background Art

[0002] As an efficient 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 of batteries during charging and discharging has become particularly important and directly affects the design of battery thermal management systems. Too high battery temperature will not only accelerate its aging and shorten its service life, but may also 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 thermal management system of batteries. At present, methods such as adiabatic acceleration calorimetry and isothermal calorimetry, although they can provide high-precision results, rely on complex test equipment and long test time, resulting in high test costs; and simple measurement methods, such as calculating heat generation and heat generation power by 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 is easy to cause large measurement errors. Therefore, the development of a fast, low-cost and widely popularized battery heat generation measurement method has become an urgent need in the current technical field. Summary of the invention

[0003] The present invention provides a fast and low-cost method for measuring heat generation during charge and discharge of lithium-ion batteries, aiming to solve the problems of complex equipment, high cost and difficulty in promotion in existing measurement methods. By optimizing the measurement method, the present invention avoids the reliance of traditional precise measurement methods on harsh test conditions, greatly reduces the test cost, and significantly improves the test efficiency.

[0004] A fast and low-cost method for measuring heat generation during charging and discharging of a lithium-ion battery, comprising the following steps:

[0005] Step 1: Completely immerse the lithium-ion battery under test in the liquid medium, ensure that the temperature of the battery and the liquid medium are the same by stirring, record the temperature of the liquid medium at this time as the initial temperature, and simultaneously record the volume of the liquid medium.

[0006] Step 2: Apply charge and discharge conditions to the lithium-ion battery under test, and keep the temperature of the liquid medium uniform by stirring. During the charge and discharge process, measure and record the battery temperature in real time until the charge and discharge conditions are completed and the temperature of the battery and the liquid medium are the same. Record the temperature of the liquid medium at this moment as the termination temperature.

[0007] Step 3: Based on the volume and volume specific heat capacity of the liquid medium in the first step and the temperature data obtained in step 2, use formula (1) to calculate the measured value of the heat generation of the battery:

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

[0009] Among them, Q measured is the measured value of heat generation of the battery, c V is the volume specific heat capacity of the liquid medium, V is the volume of the liquid medium, T end and T start are the final temperature and initial temperature of the liquid medium respectively. Use formula (2) to calculate the measured value of the heat generation power of the battery:

[0010]

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

[0012] Step 4: Use the heat generation standard sample and the same test conditions to measure and calculate the heat generation correction value of the battery.

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

[0014] Next, the control standard sample releases heat according to the thermal power calculated by formula (3) until the duration of the charge and discharge condition of the battery under test is reached:

[0015]

[0016] Among them, q standard is the thermal power of the standard sample, t is the 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 the second step), E eq is the equilibrium electromotive force of the battery under test;

[0017] Then, during the heat release process of the standard sample, the temperature of the liquid medium is kept uniform by stirring until the heat release of the standard sample ends and the temperature of the standard sample and the liquid medium are the same, and the temperature of the liquid medium at this moment is measured and recorded as the end temperature;

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

[0019]

[0020] Where Q adjusted is the heat generation correction value, τ is the charge and discharge duration of the tested battery, T standard,end is the end temperature of the liquid medium in the correction test, and the meanings of other symbols are the same as above. The heat generation power correction value is calculated according to formula (5):

[0021]

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

[0023] Step 5: Based on 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 under test according to formula (6):

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

[0025] Among them, Q real is the true value of the heat generation of the lithium-ion battery under test. Calculate the true value of the heat generation power of the lithium-ion battery under test according to formula (6):

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

[0027] Among them, q real (t) is the true value of the heat generation power of the lithium-ion battery under test. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The present invention is a flowchart of a method for measuring heat generation during charging and discharging of a lithium-ion battery according to an embodiment of the present invention.

[0029] Figure 2 Schematic diagram of a device for measuring heat generation during charging and discharging of a lithium-ion battery in an embodiment of the present invention.

[0030] Figure 3 It is a charge and discharge condition curve diagram of a lithium-ion battery in an embodiment of the present invention.

[0031] Figure 4 Schematic diagram of the liquid medium temperature measurement result in an embodiment of the present invention.

[0032] Figure 5 This is a heat generation power curve of a standard sample in an embodiment of the present invention.

[0033] Figure 6 This is a heat generation power curve of a calibrated lithium-ion battery in an embodiment of the present invention. DETAILED DESCRIPTION

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

[0035] like Figure 1 As shown, a fast and low-cost method for measuring heat generation during charging and discharging of lithium-ion batteries includes the following steps:

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

[0037] S2. Apply the following to the lithium-ion battery under test: Figure 3 In the charging and discharging conditions shown, the stirring device continues to run at a speed of 300 rpm to keep the temperature of the liquid medium uniform. During the complete charging and discharging process, the temperature of the battery is measured and recorded in real time until the charging and discharging conditions are completed and the temperature of the battery and the liquid medium is the same, such as Figure 4 At this time, the temperature of the liquid medium is 30.8°C, which is used as the termination temperature.

[0038] S3. According to the volume and volume specific heat capacity of the liquid medium recorded in step S1, and the initial temperature and end temperature data obtained in step S2, the heat generation measurement value of the battery is calculated according to formula (1):

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

[0040] S4. In order to calibrate the heat generation measurement value, replace the battery under test with a standard sample with the same shape as the battery under test and with controllable heat generation power. Figure 2 Calibration measurements were performed in the arrangement shown.

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

[0042] S42. The control standard sample releases heat according to the heat power calculated by formula (3) until the charge and discharge duration of the battery under test is reached, such as Figure 5 shown.

[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 and the liquid medium are the same. At this time, the temperature of the liquid medium is 30.2°C, which is recorded as the end temperature.

[0044] S44. Calculate the heat generation correction value of the standard sample according to formula (4):

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

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

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

[0048] According to formula (7), the true value of the heat generation power of the lithium-ion battery under test is calculated, as follows: Figure 6 shown.

Claims

1. A fast and low-cost method for measuring heat generation during charging and discharging of lithium-ion batteries, characterized in that: The following steps are involved: Step 1: Immerse the lithium-ion battery under test completely in the liquid medium, ensure that the temperature of the battery and the liquid medium are the same 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 charge and discharge conditions to the lithium-ion battery under test, and keep the temperature of the liquid medium uniform by stirring. During the charge and discharge process, measure and record the battery temperature in real time until the charge and discharge conditions are completed and the temperature of the battery and the liquid medium are the same. Record the temperature of the liquid medium at this moment as the termination temperature. Step 3: Based on the volume and volume specific heat capacity of the liquid medium in step 1 and the temperature data obtained in step 2, use formula (1) to calculate the measured value of the heat generation of the battery, and use formula (2) to calculate the measured value of the heat generation power of the battery: Q measured =c V V(T end -T start ), (1) Among them, Q measured is the measured value of heat generation of the battery, c V is the volume specific heat capacity of the liquid medium, V is the volume of the liquid medium, T end and T start are the final temperature and initial temperature of the liquid medium, q measured (t) is the measured value of the heat generation power 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 under test and controllable heat generation power to replace the batteries 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, the true heat generation value of the lithium-ion battery under test is obtained.

2. A fast and low-cost lithium-ion battery charge and discharge heat generation measurement method as claimed in claim 1, characterized in that: The "liquid medium" in step 1 is further defined as a liquid medium with good thermal conductivity and no chemical reaction with lithium-ion battery materials, preferably thermal oil, to ensure the accuracy and safety of the measurement.

3. A fast and low-cost lithium-ion battery charge and discharge heat generation measurement method as claimed in claim 1, characterized in that: The "stirring rate" in step 2 is adjusted according to the volume and viscosity of the liquid medium to ensure the uniformity of temperature distribution in the liquid medium during the entire charging and discharging process, so as to reduce the measurement error caused by the temperature difference of the medium.

4. A fast and low-cost lithium-ion battery charge and discharge heat generation measurement method as claimed in claim 1, characterized in that: The step 4 of "using a standard sample with the same shape as the lithium-ion battery to be tested and with controllable heat generation power to replace the batteries in step 1 and step 2, measuring under the same liquid medium and initial temperature conditions, and calculating the heat generation correction value of the battery" further includes the following steps: Step 41: Replace the lithium-ion battery under test with a standard sample of the same shape and controllable heat generation power, place it in the same liquid medium with the same initial temperature and the same volume, and ensure that the temperature of the standard sample and the liquid medium are the same by the same stirring rate; Step 42: The control standard sample releases heat according to the thermal power calculated by formula (3) until the duration of the charge and discharge condition of the battery under test is reached: Among them, q standard is the thermal power of the standard sample, t is the 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 by step 2), E eq is the equilibrium electromotive force of the battery under test; Step 43: During the heat release process of the standard sample, the temperature of the liquid medium is kept uniform by stirring until the heat release of the standard sample ends and the temperature of the standard sample and the liquid medium are the same, and the temperature of the liquid medium at this moment is measured and recorded as the end temperature; Step 44: Calculate the heat generation correction value according to formula (4), and calculate the heat generation power correction value according to formula (5): Where Q adjusted is the heat generation correction value, τ is the charge and discharge duration of the tested battery, T standard,end is the end temperature of the hot medium in the calibration 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 calibration test, and the meanings of other symbols are the same as above.

5. A fast and low-cost lithium-ion battery charge and discharge heat generation measurement method as claimed in claim 1, characterized in that: The step 5 of "obtaining the true value of heat generation of the lithium-ion battery under test according to the battery heat generation measurement value calculated in step 3 and the battery heat generation correction value calculated in step 4" further includes 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, the true value of the heat generation of the lithium-ion battery under test is calculated according to formula (6), and the true value of the heat generation power of the lithium-ion battery under test is calculated according to formula (7): Q real =Q measured +Q adjusted , (6) q real (t)=q measured (t)+q adjusted (t), (7) Among them, Q real is the true value of 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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