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 Yury Gogotsi, PhD. In a
piece published in Science, Gogotsi, who is the head of the A.J. 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 Patrice Simon, PhD, of the Université Paul Sabatier in Toulouse, France,
is entitled “True Performance Metrics in Electrochemical Energy Storage.”
“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 says. “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
says. “Although such plots are useful for comparing fully packaged commercial
devices, they might predict unrealistic performance for packaged cells from
extrapolation of small amounts of materials.”
Gogotsi and Simon have a long-time
research collaboration, investigating materials for supercapacitors.