Method for evaluating residual life of supercapacitor in different working states
By assessing the lifespan of supercapacitors in different states and combining the Arrhenius equation with parameter correction, the problem of inaccurate lifespan prediction in existing technologies is solved, achieving low-cost and efficient lifespan assessment.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- TSINGHUA UNIVERSITY
- Filing Date
- 2023-12-07
- Publication Date
- 2026-05-29
AI Technical Summary
Existing technologies struggle to accurately predict the lifespan of supercapacitors in practical applications, especially under complex stress and environmental conditions. Traditional methods are costly and time-consuming, and fail to comprehensively consider the effects of factors such as temperature and voltage.
By determining the charging and discharging frequency of the supercapacitor, it is divided into float charging state and cyclic state. Relevant parameters are collected, and a lifetime assessment model based on the Arrhenius equation is established. Factors such as temperature, voltage, and current are considered, voltage correction is performed, and DC or cyclic lifetime is calculated.
A more accurate and low-cost life prediction method is provided, which is applicable to supercapacitors under different operating conditions, reducing time and economic costs and improving the accuracy of life assessment.
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Figure CN117688325B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of energy storage technology, specifically relating to a method for evaluating the remaining lifespan of supercapacitors under different operating conditions. Background Technology
[0002] The rapid development of electronic devices has led to an increasing demand for high-performance energy storage solutions. Traditional chemical batteries have limited lifespan, slow charge / discharge rates, and potential environmental risks, which restrict their use in many applications. To meet the demands for rapid charge / discharge, improve lifespan, and reduce environmental risks, supercapacitors are a new type of energy storage device that bridges the gap between traditional capacitors and rechargeable batteries. They possess the rapid charge / discharge characteristics of capacitors while also exhibiting the energy storage properties of batteries, making them a highly efficient, practical, and environmentally friendly new energy storage component. Supercapacitors have introduced a new energy storage technology with enormous potential.
[0003] Supercapacitors have relatively low individual cell voltage and energy density. Large-scale energy storage systems require numerous cells connected in series and parallel. However, supercapacitors suffer from inconsistent individual cell parameters, leading to uneven temperature distribution within the module and inconsistent charging voltages between cells. These issues collectively contribute to the aging process of supercapacitors. Supercapacitors are physical energy storage devices. Compared to other electrochemical energy storage devices, ideal supercapacitors theoretically do not undergo any chemical reactions during charging and discharging, thus their lifespan is nearly unlimited. However, in reality, due to impurities introduced by manufacturing processes and material preparation, the lifespan of supercapacitors is affected by conditions such as temperature, voltage, humidity, and vibration. Temperature and voltage, in particular, have a significant impact on supercapacitor lifespan. When supercapacitors are used in module groups as power or auxiliary power systems in complex electronic systems, their remaining lifespan directly affects the reliability and safety of the entire system.
[0004] Traditional lifespan assessment methods typically involve time-intensive experiments and simulations. Current methods for predicting the remaining lifespan of supercapacitors mainly fall into two categories: one is prediction through simulating the internal aging mechanisms of supercapacitors; the other relies on large amounts of data and uses neural network models for prediction. These methods are costly and time-consuming. Furthermore, in the patent document "A method, device, and electronic device for predicting the remaining lifespan of a supercapacitor," to meet the needs of existing supercapacitor lifespan prediction technologies, this application provides a method for predicting the remaining lifespan of a supercapacitor, including: combining a hybrid genetic algorithm (HGA) with a long short-term memory (LSTM) neural network to calculate the optimal solution for the number of hidden layer units and the probability of random dropout in the LSTM; using this as the value of the number of hidden layer units and the dropout probability to train the LSTM; and using the trained LSTM to predict the remaining lifespan of the supercapacitor. The above methods are insufficient to accurately predict the lifespan of supercapacitors in practical applications because complex stress and environmental conditions are often difficult to fully simulate. Therefore, it is necessary to propose a new and more effective supercapacitor lifespan assessment method to more accurately predict the lifespan of supercapacitors in practical applications while reducing costs and time. Summary of the Invention
[0005] The purpose of this invention is to propose a method for evaluating the remaining life of supercapacitors under different operating conditions, characterized by the following steps:
[0006] Step 1: Determine whether the charging and discharging frequency of the supercapacitor meets the threshold condition based on the actual application scenario.
[0007] Step 2: Based on the charging and discharging frequency, the supercapacitor is divided into different working states, including float charging state and cyclic state, and the working parameters in the product manual are determined for each state.
[0008] Step 3: Collect parameter information during the charging and discharging process of the supercapacitor under different operating conditions;
[0009] Step 4: Perform voltage correction based on the peak and valley voltages during the charging and discharging process;
[0010] Step 5: Establish a lifetime assessment model based on the Arrhenius equation, and calculate the DC or cycle life of the supercapacitor based on the model.
[0011] In step 1, it is determined whether the charging and discharging frequency f of the supercapacitor meets the threshold condition based on the actual application scenario, as follows:
[0012] In practical applications of supercapacitors, the charging and discharging frequency f is used to determine whether it meets the threshold condition. If f ≤ f0, it is in a constant voltage floating charge state, and the lifespan of this state is called the DC lifespan. If f > f0, it is in a charge and discharge cycle state, and the lifespan of this state is called the cycle lifespan. The critical frequency f0 depends on the model of the supercapacitor.
[0013] In step 2, the supercapacitor is divided into different working states according to the charging and discharging frequency f, including float charging state and cyclic state. The working parameters are determined from the product manual, as follows: For DC life, the parameters of the supercapacitor are determined, including the estimated life under accelerated aging conditions, the ambient temperature under accelerated aging conditions, and the rated voltage. For cyclic life, the parameters that need to be determined are the thermal impedance of the product, the DC equivalent series internal resistance, the number of cycles under known accelerated aging conditions, the voltage range during charge and discharge cycles, the effective value of the charge and discharge current, and the duty cycle of the square wave current. All of the above parameters can be found directly from the product manual.
[0014] In step 3, parameter information during the charging and discharging process of the supercapacitor is collected under different operating conditions. Specifically, when assessing the DC life of the supercapacitor, the ambient temperature and actual voltage during actual use need to be collected. When assessing the cycle life, in addition to the above parameters, the highest and lowest voltage values, actual charging and discharging current values, and actual operating square wave current duty cycle also need to be collected.
[0015] In step 4, voltage correction is performed based on the highest and lowest voltage values during the charging and discharging process, as detailed below:
[0016] The effect of voltage on cycle life is similar to that of DC life. Since different voltages have different effects on life, different voltage ranges need to be corrected. During the charging and discharging process, the voltage is in a fluctuating process. The voltage range is corrected to the standard voltage V using the following formula (1). c :
[0017]
[0018] Among them, V c Indicates the corrected standard voltage; V h This indicates the highest voltage value during charging and discharging; V l This indicates the lowest voltage value during the charging and discharging process.
[0019] Step 5, which involves establishing a lifetime assessment model based on the Arrhenius equation, calculates the DC / cycle lifetime of the supercapacitor using the model, as detailed below:
[0020] The estimated DC lifetime L of a supercapacitor is mainly affected by ambient temperature and applied voltage, as described in formula (2):
[0021]
[0022] Where L is the estimated DC lifespan; L0 is the known lifespan under accelerated aging conditions (found in the product manual); T0 is the ambient temperature under accelerated aging conditions; T a V represents ambient temperature. r V is the rated voltage; V is the actual voltage.
[0023] The cycle life of supercapacitors is mainly affected by ambient temperature, cooling method, current magnitude, voltage range, and depth of charge and discharge. Among these factors, the impact of ambient temperature on cycle life is similar to that on DC life. The impact of current magnitude on life is mainly due to the heat generated by the power consumed by the internal resistance during charging and discharging, causing the product temperature to be higher than the ambient temperature. Different cooling methods result in different temperature rises of the product under the same current conditions.
[0024] Based on the actual current value measured during the charging and discharging process in step 3, the effective value of the current is calculated according to different current waveforms; if the current waveform is a harmonic, the effective value of the current I is calculated as follows:
[0025]
[0026] If the current waveform is a square wave, the effective value of the current I is calculated as follows:
[0027]
[0028] Among them, I P T1 represents the current amplitude; T2 represents the pulse width and duration of the square wave waveform; T2 represents the entire waveform period.
[0029] During a charge-discharge cycle, the power P consumed by the internal resistance is:
[0030] P = I 2 ×R (5)
[0031] Where I is the effective value of the current during charging and discharging; R is the DC equivalent series internal resistance of the product; and the temperature change ΔT of the product is:
[0032] ΔT=P×R th (6)
[0033] Where ΔT represents the temperature change of the product; R th The thermal resistance of the product;
[0034] In an open environment without any cooling measures, the thermal impedance of the product can be found in the product manual. If the product has added cooling measures, the actual temperature rise of the product needs to be measured. If the temperature rise of the product under a certain effective current condition is known, the temperature rise of the product under the actual effective current condition can be calculated using formula (7):
[0035]
[0036] Where I0 is the known effective current; I is the actual effective current; ΔT0 is the temperature rise of the product under the condition of the known effective current I0;
[0037] For the lifetime assessment model of a supercapacitor under cyclic conditions, the estimated cyclic lifetime N is:
[0038]
[0039] Where N is the estimated cycle life; N0 is the known number of cycles under accelerated aging conditions, which can be found in the product manual; ΔU0 is the voltage range during charge-discharge cycles under accelerated aging conditions; ΔU is the actual charge-discharge voltage range; I0 is the RMS value of the charge-discharge current under accelerated aging conditions; I is the actual RMS value of the charge-discharge current; η0 is the duty cycle of the square wave current under accelerated aging conditions; η is the actual operating duty cycle of the square wave current; T is the ambient temperature; ΔT is the temperature rise under actual conditions; V c0 To accelerate aging, the standard voltage after correction; V c1 This is the actual corrected standard voltage.
[0040] Compared with the prior art, the beneficial effects of this invention are:
[0041] (1) Various factors affecting the lifespan of supercapacitors were comprehensively considered, including temperature, voltage range, current magnitude, depth of charge and discharge, etc., and lifespan assessment methods for different application scenarios were designed.
[0042] (2) A method is proposed to correct the voltage range to the standard voltage when the voltage changes during the charging and discharging process under cyclic conditions. Attached Figure Description
[0043] Figure 1 A flowchart for evaluating the lifespan of a supercapacitor under different conditions.
[0044] Figure 2 The diagrams show two typical current waveforms, where a represents a harmonic current waveform and b represents a square wave current waveform.
[0045] Figure 3 This is a graph showing the change in capacity over aging time at different temperatures.
[0046] Figure 4This is a graph showing the relationship between the lifespan of a supercapacitor and the applied voltage.
[0047] Figure 5 This is a comparison chart of DC life assessment and actual measurement of supercapacitors.
[0048] Figure 6 This is a comparison chart of supercapacitor cycle life assessment and actual measurement. Detailed Implementation
[0049] This invention proposes a method for evaluating the remaining life of a supercapacitor under different operating conditions, comprising the following steps:
[0050] Step 1: Determine whether the charging and discharging frequency of the supercapacitor meets the threshold condition based on the actual application scenario.
[0051] Step 2: Based on the charging and discharging frequency, the supercapacitor is divided into different working states, including float charging state and cyclic state, and the working parameters are determined from the product manual.
[0052] Step 3: Collect parameter information during the charging and discharging process of the supercapacitor under different operating conditions;
[0053] Step 4: Perform voltage correction based on the peak and valley voltages during the charging and discharging process.
[0054] Step 5: Establish a lifetime assessment model based on the Arrhenius equation, and calculate the DC or cycle life of the supercapacitor based on the model.
[0055] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.
[0056] like Figure 1 As shown, the method for evaluating the remaining life of a supercapacitor under different operating conditions includes the following steps:
[0057] Step 1: Determine whether the charging and discharging frequency of the supercapacitor meets the threshold condition based on the actual application. Specifically, it is necessary to determine the supercapacitor state under different applications. The supercapacitor state is divided into two categories: float charge state and cyclic state. In the float charge state, the charging and discharging frequency is low, and the product is in a constant voltage and constant temperature state. This lifespan is called DC lifespan, typically measured in hours. In the cyclic state, the supercapacitor's charging and discharging frequency is high, and the product is in a charge-discharge cycle state. This lifespan is called cyclic lifespan, expressed by the number of cycles. Therefore, before assessing the supercapacitor's lifespan, it is necessary to determine whether the threshold condition is met based on the different charging and discharging frequencies f in the actual application. If f ≤ f0, it is in a constant voltage float charge state; if f > f0, it is in a charge-discharge cyclic state. This critical frequency f0 depends on the supercapacitor model; refer to the supercapacitor's datasheet. For example, the cyclic state frequency of a 3000F supercapacitor manufactured by CRRC is 1kHz.
[0058] Step 2: Based on the charging and discharging frequency, the supercapacitor is divided into different operating states, including float charging state and cyclic charging state. The operating parameters of each state are then determined according to the product manual, as follows:
[0059] The DC lifespan of a supercapacitor is primarily affected by ambient temperature and applied voltage. First, the parameters of the supercapacitor must be determined, including the estimated lifespan under accelerated aging conditions, ambient temperature, and rated voltage. For example, the standard test conditions for product A are: standard atmospheric pressure, ambient temperature of 65°C, relative humidity less than 60%, and accelerated aging voltage of 2.7V. Under these conditions, the estimated lifespan of the supercapacitor is 1500 hours.
[0060] The cycle life of a supercapacitor is mainly affected by ambient temperature, cooling method, current magnitude, voltage range, and depth of charge / discharge. To determine cycle life, parameters that need to be determined include the product's thermal resistance, DC equivalent series resistance, known number of cycles under accelerated aging conditions, voltage range during charge / discharge cycles, effective value of charge / discharge current, and square wave current duty cycle. For example, the standard test conditions for product B are: standard atmospheric pressure, ambient temperature of 25℃, relative humidity less than 60%, and accelerated aging voltage of 2.7V. Under these conditions, the estimated life of the supercapacitor is 1 million cycles. Under these conditions, the supercapacitor's thermal resistance is 3.1℃ / W, its DC equivalent series resistance is 0.22mΩ, and its effective value of charge / discharge current is 134A.
[0061] Step 3: Collect parameter information during the charging and discharging process of the supercapacitor under different operating conditions, as detailed below:
[0062] Before assessing the lifespan of a supercapacitor, it is necessary to collect charging and discharging parameters under various conditions. The float charge / discharge test method is as follows: Initialize the supercapacitor by discharging it; place the supercapacitor at several preset temperatures for 12 hours; charge each supercapacitor cell at rated power with constant power until the voltage of each cell reaches the rated maximum operating voltage, then let it rest for 10 seconds; discharge each supercapacitor cell at rated power with constant power until the voltage of each cell reaches the rated minimum operating voltage, then let it rest for 10 seconds; charge each supercapacitor cell at rated power with constant power to the float charge voltage and maintain this voltage for 168 hours; place it at room temperature for 24 hours, and test the supercapacitor capacity. Repeat the above operations until the lifespan termination condition of the capacitance value being less than 80% of the initial capacitance value is met. During the accelerated aging test, a certain operating temperature and voltage can be set to keep the supercapacitor in a float charge state under these conditions.
[0063] The cyclic charge-discharge test method is as follows: The supercapacitor is first initialized and discharged; it is then charged with a constant current to the charging termination voltage of a single capacitor cell and left to stand for 10 seconds; the supercapacitor is then discharged with a constant current to the discharge termination voltage under different charge-discharge ranges and left to stand for 10 seconds; after each 500 cycles, it is left to stand for 12 hours, and the capacitance value of the supercapacitor is detected. The above operation is repeated until the lifespan termination condition of the capacitance value being less than 80% of the initial capacitance value is met.
[0064] The testing method for the current and duty cycle of a supercapacitor in a square wave waveform is as follows: Connect a signal generator to the supercapacitor and set it to generate a square wave current signal. Connect a current measuring instrument to measure the current waveform. An oscilloscope can be used to observe and record the current waveform (e.g., ...). Figure 2 The diagram shows two typical current waveforms, where a is the harmonic current waveform and b is the square wave current waveform. Through the above operations, the current amplitude of the supercapacitor in cyclic mode and the duty cycle of the square wave current can be obtained.
[0065] Step 4: Perform voltage correction based on the highest and lowest voltage values during the charging and discharging process, as detailed below:
[0066] Based on the voltage test results during the charge-discharge cycle in step 3, the highest and lowest voltage values can be obtained, representing the depth of charge and discharge of the supercapacitor. The effect of voltage on cycle life is similar to that of DC life. Since different voltages have different effects on lifespan, different voltage ranges need to be corrected. During the charge-discharge process, the voltage fluctuates; the voltage range is corrected to a standard voltage using the following formula:
[0067]
[0068] Among them, V c Indicates the corrected standard voltage; Vh This indicates the highest voltage value during charging and discharging; V l This represents the minimum voltage value during the charging and discharging process; z is the voltage acceleration coefficient, which will be analyzed in detail later.
[0069] Step 5: Establish a lifetime assessment model based on the Arrhenius equation, and calculate the DC or cycle life of the supercapacitor according to the model, as follows:
[0070] The Arrhenius equation for the reliability response rate is as follows:
[0071]
[0072] Where k is the reaction rate; P represents the amount of reactant; A is the pre-exponential factor; and R is the Boltzmann constant, 8.617385 × 10⁻⁶. -5 eV / K; T is absolute temperature; E a It is represented as activation energy.
[0073] In the Arrhenius equation, the pre-exponential factor is a constant used to describe the probability of reactant molecules meeting and forming reaction products. It includes various influencing factors, such as collision frequency and orientation factor, reflecting the likelihood of the reaction occurring. Activation energy refers to the energy barrier that must be overcome for charge transfer between the electrode surface and the electrolyte interface during the charging and discharging process of a supercapacitor. It is an important parameter describing the energy storage and release capability of a supercapacitor. To obtain the activation energy of a supercapacitor, an accelerated temperature lifetime experiment can be conducted, keeping the actual applied voltage constant and using the experimental temperature as a parameter. The specific steps are as follows: Place the supercapacitor in a high-temperature chamber at different temperatures and maintain a floating charge state at the rated voltage. At regular intervals, remove the supercapacitor and measure its capacitance or resistance. Fit the measured data to obtain its capacity degradation curve. Selecting two different experimental temperatures T1 and T2 and their corresponding fitted capacitor lifetimes t1 and t2 can be obtained by taking the logarithm of the Arrhenius equation.
[0074]
[0075] The activation energy was determined based on the above accelerated lifespan testing procedures, and a 3000F single-cell supercapacitor (product A) from a certain company was selected. The Boltzmann constant is 8.617385 × 10⁻⁶. -5 eV / K, the experiment measured two different experimental temperatures of 65℃ and 60℃. The time it took for the supercapacitor's capacitance to fall below 80% of its initial capacitance was defined as its lifespan. At these experimental temperatures, the supercapacitor's lifespan was 1500h and 2364.2h. Figure 3 The figure shows the capacity change with aging time at different temperatures. The activation energy E can be calculated from the above equation. aIt is 0.8833681 eV, therefore E a / R=10251.
[0076] While specific methods for calculating the activation energy through lifetime acceleration experiments have been documented, considering only the temperature effect on the lifetime of supercapacitors in practical applications is insufficient. The DC lifetime of supercapacitors is affected not only by ambient temperature but also by the applied voltage. Therefore, a voltage acceleration factor is introduced in addition to the temperature acceleration factor, as described in the formula:
[0077]
[0078] Where L is the estimated DC lifespan; L0 is the known lifespan under accelerated aging conditions, which can be found in the instruction manual; E a is the activation energy; R is the Boltzmann constant; T0 is the ambient temperature under accelerated aging conditions; T a The actual operating ambient temperature; z is the voltage acceleration coefficient; V r V is the rated voltage; V is the actual voltage.
[0079] To obtain the voltage acceleration factor of a supercapacitor, the actual temperature can be kept constant during the experiment, and the applied voltage can be used as a parameter to conduct an accelerated life test. The specific steps are as follows: Place the supercapacitor in a high-temperature chamber at the same temperature of 65°C, and maintain it in a floating charge state under different applied voltages. At regular intervals, remove the supercapacitor and measure its capacitance or resistance value. Fit the measured data to obtain its capacitance degradation curve. Select two different experimental voltages V1 and V2 and their corresponding fitted values to obtain the capacitor lifetimes L1 and L2. Under the accelerated aging conditions, the known lifetime and temperature acceleration factor remain constant. Taking the logarithm of both sides yields:
[0080] ln L=ln C+(Vr-V)ln z
[0081] Where L represents the estimated DC lifetime obtained from the fitting; constant term Therefore, it can be seen that the logarithm of the estimated DC lifetime of the supercapacitor is linearly related to the applied voltage. The voltage acceleration factor can be obtained by plotting the graph and using the slope.
[0082] To determine the voltage acceleration coefficient, product A used in deriving the activation energy can still be selected. From the above analysis, the constant term C = L0 = 1500h. To improve the reliability of this coefficient, the lifetimes of the supercapacitors obtained by selecting experimental voltages of 2.1V, 2.3V, 2.5V, and 2.7V are 17085.9h, 7593.7h, 3375.0h, and 1500h, respectively. Therefore, it can be concluded that... Figure 4 Based on the slope of the graph, z = 1.5 10≈57.67.
[0083] Therefore, the lifetime assessment model for supercapacitors under DC conditions is described as follows:
[0084]
[0085] For cyclic operation, the lifespan of a supercapacitor is mainly affected by ambient temperature, cooling method, current magnitude, voltage range, and depth of charge / discharge. Among these factors, the impact of ambient temperature on lifespan during cyclic operation is similar to that during DC operation. The impact of current magnitude on lifespan is mainly due to the heat generated by the power consumed by the internal resistance during charging and discharging, causing the product temperature to be higher than the ambient temperature. Different cooling methods result in different temperature rises for the product under the same current conditions.
[0086] Based on the actual current amplitude measured during the charging and discharging process in step 3, the effective value of the current can be calculated according to different current waveforms; if the current waveform is a harmonic, the effective value of the current is calculated as follows:
[0087]
[0088] If the current waveform is a square wave, the effective value of the current is calculated as follows:
[0089]
[0090] Among them, I P This refers to the current amplitude. This represents the duty cycle of the square wave.
[0091] During a charge-discharge cycle, the power consumed by the internal resistance is:
[0092] P = I 2 ×R (5)
[0093] Where I is the effective value of the current during charging and discharging; R is the DC equivalent series internal resistance of the product; and the temperature change of the product is:
[0094] ΔT=P×R th (6)
[0095] Where ΔT represents the temperature change of the product; R th The thermal resistance of the product;
[0096] In an open environment without any cooling measures, the product's thermal impedance can be found in the instruction manual. If cooling measures are added, the actual temperature rise needs to be measured. If the temperature rise under a certain effective current condition is known, it can be calculated using the following formula:
[0097]
[0098] Where I0 is the known effective current; I is the actual effective current; ΔT0 is the temperature rise of the product under the known effective current I0; according to the parameters given in the specification, the thermal resistance of the supercapacitor is 3.1℃ / W, the DC equivalent series internal resistance is 0.22mΩ, and the effective value of the charging and discharging current is 134A. Therefore, ΔT0 = 12.246℃ can be obtained.
[0099] The lifetime assessment model for supercapacitors under cyclic conditions is as follows:
[0100]
[0101] Where N is the estimated cycle life; N0 is the known number of cycles under accelerated aging conditions, which can be found in the instruction manual; ΔU0 is the voltage range during charge-discharge cycles under accelerated aging conditions; ΔU is the actual charge-discharge voltage range; I0 is the RMS value of the charge-discharge current under accelerated aging conditions; I is the actual RMS value of the charge-discharge current; η0 is the duty cycle of the square wave current under accelerated aging conditions; η is the actual operating duty cycle of the square wave current; T is the ambient temperature; ΔT is the temperature rise under actual conditions; V c0 This is the rated, calibrated standard voltage; V c1 This is the actual corrected standard voltage.
[0102] The life assessment method was validated using the different experimental methods employed in step 3: For product A, a float charge accelerated aging test was conducted, specifically including:
[0103] (1) Initialize the discharge of the supercapacitor;
[0104] (2) Charge the supercapacitor cell at the rated power at a constant power until the voltage of the supercapacitor cell reaches the rated maximum working voltage of 2.7V, and then let it stand for 10 seconds.
[0105] (3) Discharge the supercapacitor cell at the rated power at a constant power until the voltage of the supercapacitor cell reaches the rated minimum operating voltage of 1.35V, and then let it stand for 10 seconds.
[0106] (4) Set three accelerated aging operating temperatures: 55, 60, and 65℃ and three float charging voltages: 2.55, 2.6, and 2.7V, for a total of nine operating conditions;
[0107] (5) In each of the above operating conditions, after being placed at its operating temperature for 12 hours, the supercapacitor is charged to the float charge voltage at the rated power and held at that voltage for 168 hours.
[0108] (6) Place the supercapacitor at room temperature for 24 hours, test its capacitance, and repeat operation (5) until the capacitance value is less than 80% of the initial capacitance value, thus ending its lifespan. The experimental results and accelerated lifespan data for the above nine operating conditions are shown in Table 1.
[0109] According to the product manual for product A in step 2, the DC lifespan of the supercapacitor under accelerated aging conditions is approximately 1500 hours, the ambient temperature is 65℃, and the accelerated aging voltage is 2.7V. Based on equation (2), the predicted lifespan of the final product under certain temperature and voltage conditions can be calculated, thus avoiding the need for full life-cycle performance testing of the final product. The lifespan assessment results of the supercapacitor calculated using equation (2) are shown in Table 2.
[0110] Table 1. Lifetime of supercapacitors measured under different operating conditions.
[0111]
[0112] Table 2. Lifetime of supercapacitors evaluated by this method under different operating conditions.
[0113]
[0114] According to the product manual of product B in step 2, the cycle life of the supercapacitor under accelerated aging conditions is about 1 million cycles (ten years), the ambient temperature is 25℃, the accelerated aging voltage is 2.7V, the accelerated aging current is 134A, the duty cycle of the square wave current under accelerated aging conditions is 0.4, and the voltage range during charge and discharge cycles is 2.7V.
[0115] Since the above content has analyzed the influence of operating temperature and voltage on the life of supercapacitors, the following analysis will only focus on the influence of charge and discharge range, effective current value, and square wave current duty cycle on the supercapacitor cycle life assessment process. To shorten the experimental time, product B was subjected to a cyclic charge and discharge accelerated aging test at 65℃: (1) Select different charge and discharge voltage ranges ΔU1 and ΔU2, set two effective values of accelerated aging charge and discharge current: I1 and I2, and two square wave current duty cycles of 0.6 and 0.4; (2) In each of the above operating conditions, initial discharge was performed first; (3) With a constant capacitor current I p1 Charge to the charging termination voltage of the capacitor cell, accelerate aging voltage V = 2.7V, and let stand for 10s; (4) The supercapacitor is charged with a constant current I p1 Discharge to the discharge termination voltage (U1=U-ΔU1) under different charge and discharge ranges respectively, and let stand for 10s; (5) after each 500 cycles, let stand for 12 hours, and check the capacitance value of the supercapacitor. Repeat steps (2) to (5) until the life termination condition of the capacitance value being less than 80% of the initial capacitance value is met. The experimental results and the accelerated life data measured under the above working conditions are shown in Table 3:
[0116] Table 3. Lifetime of supercapacitors measured under cyclic conditions.
[0117]
[0118]
[0119] According to equation (8), the predicted final product lifespan under different charging and discharging voltage ranges, current RMS values, and square wave current RMS values can be calculated (e.g., Figure 4 As shown in the figure), this avoids the need for full life cycle performance testing of the final product. The evaluation life results of the supercapacitor calculated by equation (8) are shown in Table 4.
[0120] Table 4. Calculation results of supercapacitor lifetime assessment under cyclic conditions.
[0121]
Claims
1. A method for evaluating the remaining life of a supercapacitor under different operating conditions, characterized in that, Includes the following steps: Step 1: Determine whether the charging and discharging frequency of the supercapacitor meets the threshold condition based on the actual application scenario. Step 2: Based on the charging and discharging frequency, the supercapacitor is divided into different working states, including float charging state and cyclic state, and the working parameters in the product manual are determined for each state. Step 3: Collect parameter information during the charging and discharging process of the supercapacitor under different operating conditions; Step 4: Perform voltage correction based on the peak and valley voltages during the charging and discharging process; Step 5: Establish a lifetime assessment model based on the Arrhenius equation, and calculate the DC or cycle life of the supercapacitor based on the model; Step 5 describes establishing a lifetime assessment model based on the Arrhenius equation. The DC / cycle lifetime of the supercapacitor is calculated using the model, as detailed below: DC estimated lifetime of supercapacitors The relationship between ambient temperature and applied voltage is described by formula (2): （2） in, Estimating the lifetime for DC; To accelerate the known lifespan under aging conditions, refer to the product manual. To accelerate the aging process, the ambient temperature is required. The ambient temperature; Rated voltage; This is the actual voltage; The cycle life of a supercapacitor is affected by ambient temperature, cooling method, current magnitude, voltage range, and depth of charge and discharge. Among these factors, the impact of current magnitude on life is that during the charge and discharge process, the power consumed by the internal resistance generates heat, causing the product temperature to be higher than the ambient temperature. Different cooling methods result in different temperature rises of the product under the same current conditions. Based on the actual current value measured during the charging and discharging process in step 3, calculate the effective value of the current according to different current waveforms; if the current waveform is a harmonic, the effective value of the current... The calculation is as follows: （3） If the current waveform is a square wave, then the effective value of the current is... The calculation method is as follows: （4） in, This refers to the current amplitude. The pulse width and time of the square wave waveform; The entire waveform period; Power consumed by internal resistance during charge-discharge cycles for: （5） in, This represents the effective value of the current during the charging and discharging process. The DC equivalent series internal resistance of the product; Product temperature change for: （6） in, For product temperature changes; The thermal resistance of the product; In an open environment without any cooling measures, the thermal impedance of the product can be found in the product manual. If the product has added cooling measures, the actual temperature rise of the product needs to be measured. If the temperature rise of the product under a certain effective current condition is known, the temperature rise under the actual effective current condition can be calculated using formula (7). （7） in, The effective current is known. This represents the actual effective current. To know the effective current Temperature rise of the product under the given conditions; For the life assessment model of supercapacitors under cyclic conditions, the estimated cyclic life is... for: （8） in, To estimate lifetime for cycles; To accelerate the known number of cycles under aging conditions, refer to the product manual; To accelerate the voltage range during charge-discharge cycles under aging conditions; This refers to the actual charge / discharge voltage range. To accelerate the effective value of charge and discharge current under aging conditions; This is the effective value of the actual charging and discharging current; To accelerate the duty cycle of the square wave current under aging conditions; This refers to the actual operating square wave current duty cycle. The ambient temperature; This refers to the temperature rise under actual conditions. This is the rated, calibrated standard voltage; This is the actual corrected standard voltage.
2. The method for evaluating the remaining life of a supercapacitor under different operating conditions according to claim 1, characterized in that, In step 1, it is determined whether the charging and discharging frequency f of the supercapacitor meets the threshold condition based on the actual application scenario, as follows: Based on the practical applications of supercapacitors, the charging and discharging frequency f is used to determine whether it meets the threshold condition. If the voltage is constant, then it is in a floating charge state, and the lifespan of this state is called the DC lifespan; if This indicates a charge-discharge cycle state, and the lifespan of this state is called the cycle life; critical frequency. It depends on the model of the supercapacitor.
3. The method for assessing the remaining life of a supercapacitor under different operating conditions according to claim 1, characterized in that, In step 2, based on the charging and discharging frequency f, the supercapacitor is divided into different operating states, including float charging state and cyclic charging state. The operating parameters of each state are determined from the product manual, as follows: For DC life, the parameters of the supercapacitor need to be determined, including the estimated life under accelerated aging conditions, the ambient temperature under those conditions, and the rated voltage. For cycle life, the parameters that need to be determined are the thermal impedance of the product, the DC equivalent series internal resistance, the number of cycles under accelerated aging conditions, the voltage range during charge and discharge cycles, the effective value of the charge and discharge current, and the duty cycle of the square wave current. All of these parameters can be found directly in the product manual.
4. The method for assessing the remaining life of a supercapacitor under different operating conditions according to claim 1, characterized in that, In step 3, parameter information during the charging and discharging process of the supercapacitor is collected under different operating conditions, as detailed below: When assessing the DC lifespan of a supercapacitor, it is necessary to collect the ambient temperature and actual voltage of the supercapacitor during actual use. In addition to the parameters mentioned above, when evaluating cycle life, it is also necessary to collect the highest and lowest voltage values, actual charge and discharge current values, and actual operating square wave current duty cycle during the charging and discharging process.
5. The method for assessing the remaining life of a supercapacitor under different operating conditions according to claim 1, characterized in that, In step 4, voltage correction is performed based on the highest and lowest voltage values during the charging and discharging process, as detailed below: Since different voltages have different effects on lifespan, different voltage ranges need to be corrected. During the charging and discharging process, the voltage is in a fluctuating state. The voltage range is corrected to the standard voltage using the following formula (1). : （1） in, This indicates the corrected standard voltage; This indicates the highest voltage value during the charging and discharging process; This indicates the lowest voltage value during the charging and discharging process.