Supercap Lifetime

Supercaps last longer

Ultracap-Knowledge | Rainer Hake | reading time: 5 minutes

What factors determine the service life of an ultracap?

The question of the service life of ULTRACAPs is frequently asked. Usually, the lifetime of EDLCs is given as 1 million charge cycles at 25 °C and in compli­ance with the load speci­fication. A cycle usually extends from a full charge to half the charge (Un - Un/2).

In the course of a supercap life, the capacitor loses capacity (C) and the internal resis­tance (ESR) increases. By definition, the end of life is reached when the capa­citance has dropped to 70% of its original value or the internal resis­tance has doubled.

Electronics designers are particularly interested in the question of how the service life behaves when only 25% or 50% of the full number of cycles are used, i.e. when a discharge is made to 75% or 50% of the original discharge voltage. What are the exact effects of different fre­quencies of charging and dis­charging? How is the life affected by sporadic discharge in the presence of an electro­static field and frequent discharge at high currents?

During the service life of a supercap, the capacitor loses capacitance (C) and the equivalent serial resistance (ESR) increases. The service life has reached its end when the capa­citance has fallen to 70% of its original value, or the equivalent serial resistance has doubled.

Many factors influencing the ageing process

It is a fact that the ageing process of capa­citors depends on various factors. Tempe­rature, voltage, electrical currents and time play a significant role. Another influ­encing factor is the "diffusion capacitance" and the "diffusion resistance", which are explained in more detail in this Wikipedia article [diffusion capacitance].

What influences the lifetime of ultracaps the most?

  • Ambient temperature
  • Cell voltage
  • Charge / discharge current
  • Charge cycle (charging time and breaks)

We refer to two publicly available scientific publications (see below).

Decisive influence of temperature and voltage

The service life of a SUPERCAP is mainly influenced by two parameters: the temperature and the cell voltage. Both values should be taken into account when consi­dering the service life and the layout of the system. The lower tempera­ture range of ­40°C is almost ideal for the UCs and the UCs are not signifi­cantly influ­enced by low tempe­ratures. However, the ESR increases due to the lower ionic mobility at lower tempe­ratures, which is generally compen­sated for by the self-heating during operation. The service life of the cells is severely impaired at high tempe­ratures, as is the case for normal electro­lytic capacitors. However, it is possible to counter­act the influence of the tempe­rature by reducing the cell voltage.

The following rule of thumb applies: 0.1V cell voltage equals appro­ximately 10°C. This should, however, be considered on an individual basis and taken into account when designing the system. Please see the Technical Guide of the manu­facturer for more infor­mation. The usual service life specification of 10 years given in the technical guides generally applies to room temperature and individual voltage specifications.

Lifetime of supercaps

Example of a test for high charge cycles load cycles

The service life of large energy-storage systems, such as those used in railways, buses and cranes, plays a crucial role when consi­dering the overall system costs. It is there­fore important to monitor the para­meters that deter­mine reliability (and thus service life) and to adjust them as necessary. The main para­meters that determine the service life include:

  • Cell voltage
  • Cell temperature
  • Ambient temperature
  • Current load of the cells
  • Number of cycles

The rest period plays a particularly important role for high cycle counts and large currents. As a result, the heat distri­bution in the cells and the cooling of such systems is parti­cularly important and requires precise, individual, application-based consideration.

Accelerated service-life tests

For this reason, industrial users have developed their own test methods and load cycles to best meet their requirements. These tests are designed to simulate the calculated service life across a short period of time. These acce­lerated service-life tests use values that occur in actual operation, but the values are generally confi­gured at the upper or lower limits. This allows the load cycles to be applied more quickly and with greater capacities. Potential temp­erature cycles are incor­porated at the same time. The illustration shows an example of such a load cycle.

Example of a load cycle simulation

Current scientific publications on the
subject of "Life-time of supercapacitors

  1. The article of the EPCI - European Passive Component Institute "Super­capacitor Degra­dation and Life-time" August 2022 describes in detail the effects of voltage and current through experiments with many cycles (>100,000) as well as effects of tempe­rature in the range between -35 °C to 65 °C deter­mined over 9,000 hours. It also deals with diffuse capa­citance and diffuse resistance.

  2. The dissertation by Moritz Teuber from RWTH Aachen University from June 2019 "Lifetime Assessment and Degra­dation Mecha­nisms in Electric Double-Layer Capacitors analyses chemical pro­cesses that affect the lifetime. The sup­posedly simple rules of thumb, according to which small changes in voltage double or halve the life, are questioned here. The work shows the complex inter­relation­ships between voltage, temperature and time. Different materials and properties are illuminated, also with regard to the life span. The dis­sertation gives designers a valuable guide to improving performance and lifetime.


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Why are components like ultracaps called different names?

The variety of terms is explained by the English-language terms commonly used in the electronics industry, which are often mixed with German terms or used synonymously. In some cases, manufacturers have also introduced artificial terms to better distinguish themselves from competitors. Here are the most important examples:

Double layer capacitors (DSK) are referred to synonymously as:

  • EDLC (Electric Double Layer Capacitor)
  • Supercapacitors = Supercaps
  • Ultracapacitors = Ultracaps
  • Goldcap™ [Panasonic]
  • Boostcap™  [Maxwell]
  • Greencap™  [Samwha]
  • PURIXEL™  [Pureechem] for supercap cells
  • PURETRON™  [Pureechem] for supercap modules

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