Drexel's Gogotsi Questions Accuracy of Battery Performance Metrics
November 29, 2011
Solving the mystery of prematurely dead cell phone and laptop
batteries may prove to be a vital step toward creating a
sustainable energy grid according to Drexel researcher Dr. Yury
Gogotsi. In a piece published in the November 18 edition of Science, Gogotsi, who is the head of
Drexel Nanotechnology Institute, calls for a new, standardized
gauge of performance measurement for energy storage devices that
are as small as those used in cell phones to as large as those used
in the national energy grid.
Gogotsi is one of the featured experts, along with Bill Gates,
tapped by Science to address problems that must be solved
en route to the widespread use of renewable energy. His
piece, co-authored with Dr.
Patrice Simon of the Université Paul Sabatier in Toulouse,
France, is entitled "True Performance Metrics in Electrochemical Energy
"A dramatic expansion of research in the area of electrochemical
energy storage has occurred over the past due to an ever increasing
variety of handheld electronic devices that we all use," Gogotsi
said. "This has expanded use of electrical energy in
transportation, and the need to store renewable energy efficiently
at the grid level. This process has been accompanied by the
chase for glory with the arrival of new materials and technologies
that leads to unrealistic expectations for batteries and
supercapacitors and may hurt the entire energy storage field."
The main type of energy storage device addressed in the article
is the supercapacitor. Supercapacators, which are built from
relatively inexpensive natural materials such as carbon, aluminum
and polymers, are found in devices, ranging from mobile phones and
laptop batteries to trams, buses and solar cells. While
supercapacitors tend to store less energy compared to standard
lithium-ion batteries, they have the ability to charge and
discharge energy more quickly than batteries and can be recharged a
near infinite number of times, and operate in a wider temperature
range with a high efficiency.
Typically, the performance of both batteries and
supercapacitors, is presented using Ragone plots, graphs that show
a relation between the energy density and the power density.
For example, a Rangone plot for the battery used in an electric car
shows both how far it can travel on a single charge -energy
density- and how fast the car can travel -power density. An
ideal energy storage device is expected to store plenty of energy
and do it quickly.
The issue that Gogotsi and Simon bring to light is the idea that
current metrics for grading energy storage devices, including the
Ragone plot, may not provide a complete picture of the devices'
capability. According to the researchers, other metrics, such
as a device's cycle lifetime, energy efficiency, self-discharge,
temperature range of operation and cost, must also be reported.
"This paper calls upon the community of scientists and engineers
who work on supercapacitors to present data on material performance
using metrics beyond the traditional Ragone plot," Simon
said. "Although such plots are useful for comparing fully
packaged commercial devices, they might predict unrealistic
performance for packaged cells from extrapolation of small amounts
Gogotsi and Simon have a longtime research collaboration,
investigating materials for supercapacitors. Their joint work
has received global coverage and various awards and
distinctions. Funding for the collaboration between Gogotsi
and Simon is sponsored by the Partner University Fund (PUF) which
supports innovative and sustainable partnerships between French and
US institutions of research and higher education.
Gogotsi (left) and Simon