Download Topic: F

EDLC Characterization Platform
Alexandru Vasile1), Emilian Ceuca2), Paul Svasta1), Andreea Brodeală1), Cristina Marghescu1),
Ciprian Ionescu1)
1) University POLITEHNICA of Bucharest
Faculty of Electronics, Telecommunications and Information Technology
Center for Technological Electronics and Interconnection Techniques,
2) University 1 Decembrie 1918, Alba Iulia
E-mail address: [email protected]; [email protected]
Topic: F
Presentation: P
Summary: Technological improvements have led to the development of low resistivity
materials with higher surface which are capable of storing more energy in the form of electrical
charge. These developments as well as a better theoretical understanding of the process of charge
transfer, a process that appears in double layer type materials, led to the development of
capacitors with high capacitance, known as EDLC (Electrochemical Double-Layer Capacitor). It
is important for the user to be able to predict the behaviour of the EDLC in different conditions.
This paper introduces a platform which can be used to obtain the capacitance as a function of
voltage, time or temperature.
Keywords: Electrochemical Double-Layer Capacitor, characterization platform.
Motivation
Compare with the ordinary capacitor the super capacitor present a very high capacity at a
low volume (fig.1). A simple model describes a double-layer capacitor as a capacity (C)
connected in parallel with an equivalent series resistance (ESR) and an equivalent parallel
resistance (EPR). ESR is used to model power loss due to internal heating; internal heating is an
important parameter for the charging/recharging processes. EPR models the current flow which
influences the energy storage on the long term. One method to evaluate the energy density and
the power density for super capacitors is charging them with a constant current. By charging and
discharging super capacitors repeatedly we can raise the voltage characteristic.
Fig. 1. Super capacitors (10F/2.5V)
Fig. 2. Characterization platform
Results
The characterization of an EDLC – the value of the capacitance as a function of time,
voltage or temperature - was performed using a platform developed for this type of
measurements. The block diagram of the developed platform is presented in fig.2. This platform
yields accurate results for small currents. At high currents the behaviour of the assembly highly
differs from the estimated one.
Fig. 3. The evolution of damping with frequency
Fig. 4: Charging of a super capacitor at 5 A
compared with the capacitors ideal behaviour
(dashed line)
While the stored charge is higher than the charge stored by classic components,
monitoring time is extremely high (hours or even hundreds of hours). Since this would be very
difficult to do for a human operator we have chosen to integrate the platform with an automated
monitoring system. Using this platform, characterizations such as the ones described by Zubieta
and referred to in this paper (fig.4), as well as characterizations employing the new method
introduced by the authors with a constant current sink, monitored by a computing device.
Results regarding the influence of frequency, results obtained with the above mentioned
platform, are introduced in fig. 3. In the extended paper we present results regarding the
influence of temperature and loss current on the EDLC.
References
[1]
[2]
[3]
[4]
B.E.Conway, ”Electrochemical Supercapacitors, Scientific Fundamentals and Technological
Applications”, Kluver Academic, 1999.
Patrick Johnson, Bjorn Andersson, ”Comparison of Simulation Programs for Supercapacitor
Modelling Model Creation and Verification”, 2008.
L. Zubieta and R. Bonert, “Characterization of double-layer capacitors (DLCs) for power
electronics applications”, Proc. 33rd IEEE Ind. Appl.Soc., Annu. Meet., vol. 2, pp. 1149-1154, Oct.
1998.
Anca Duta, ”Tayloring Energy Storage Capacity in Lithium Ion Batteries”, ECOST 2009.