Abstract：This article presents the factors influencing the lifespan of EDLC, including temperature, applied voltage, and voltage balancing. It explains the impact of high temperature on the lifespan of EDLC and the underlying reasons. The article analyzes the actual lifespan and temperature difference leading to a halved lifespan for different packaging forms under high-temperature conditions. Additionally, it provides insight into the relative relationship between operating voltage and lifespan. Furthermore, the article examines the balancing effects of different forms of individual cell voltages.
EDLC offer many advantages, such as high energy density, extended lifespan (up to 10 years at room temperature, surpassing traditional batteries), and an exceptionally long charge-discharge cycle life (between 500,000 to 1 million cycles, higher than batteries). These merits have led to the widespread adoption of EDLC across various domains. However, the practical usage data might deviate notably from the values provided in datasheets.
Especially when EDLC are connected in series to form a capacitor module, this configuration can accelerate the degradation of individual capacitor capacities, subsequently shortening the lifespan of the EDLC module. Thus, it is crucial to comprehend the factors influencing the lifespan of EDLC during actual applications and to take measures to mitigate these factors.
The primary factors influencing EDLC include: high-temperature environments, applied voltage, and the voltage balancing characteristics of equalization circuits.
1.Impact of High-Temperature Environments on EDLC Lifespan
Firstly, the nominal lifespan of EDLC as stated in datasheets is typically 10 years at room temperature. However, if we apply the “10-degree rule,” which is a relationship between temperature and lifespan for electrolytic capacitors, we can extrapolate that at the highest operating temperature (65°C), the lifespan would be approximately 5,475 hours, equivalent to around 7.6 months or 228 days.
However, in reality, the high-temperature lifespan of EDLC is significantly shorter than the extrapolated results. Therefore, it’s imperative to analyze the underlying causes. Upon analyzing datasheets, it becomes evident that different manufacturers of EDLC provide varying high-temperature lifespans. For instance, while one manufacturer might indicate a high-temperature lifespan of 1500 hours, another manufacturer might specify 1000 hours.
The discrepancies in high-temperature lifespans stem from differences in manufacturing standards and packaging forms. Figure 1 illustrates the diverse packaging forms among different EDLC manufacturers.
In the figure, “Left 1” and “Left 2” represent packaging forms for standard electrolytic capacitors, which are relatively cost-effective. The high-temperature lifespan for this packaging approach is approximately 1000 hours. On the other hand, the high-temperature lifespan for the packaging form depicted on the right is 1500 hours.
If the nominal lifespan at room temperature is consistently 10 years, then the room temperature to high-temperature lifespan ratio for the standard electrolytic capacitor packaging forms is 87.6. This corresponds to a temperature difference (ΔT) at which the lifespan is halved, calculated as:
Equation (1) indicates that for EDLC using standard electrolytic capacitor packaging forms, the temperature difference at which the lifespan is halved is approximately 6.2°C. Consequently, when considering an ambient temperature of 50°C, the corresponding temperature difference becomes 15°C. This is 2.43 times the 6.18°C, which means an additional factor of 2 raised to the power of 1.43. This corresponds to an actual lifespan of approximately:
This results in approximately 2694 hours of lifespan, rather than the approximately 11000 hours estimated using the 10-degree rule.
For the packaging form furthest to the right in the figure, the room temperature to high-temperature lifespan ratio is 58.4. This corresponds to a temperature difference (ΔT) at which the lifespan is halved of:
Equation (3) demonstrates that for EDLC using the packaging form depicted in the far-right of Figure 1, the temperature difference at which the lifespan is halved is approximately 5.87°C. Thus, when considering an ambient temperature of 50°C, the corresponding temperature difference becomes 15°C. This is 2.56 times the 5.87°C, which equates to an additional factor of 2 raised to the power of 1.56. This corresponds to an actual lifespan of approximately: