Environmental Engineering Reference
In-Depth Information
• High-energy efficiencies arising from electrochemical reversibility
of vanadium redox couples
• Recharge at high rates
• Uniform cell potential achieved by reuse of same solution
• Simple monitoring and maintenance; no need for monitoring and
adjustment of individual cells
• Monitoring electrolyte state of charge by using the Nernstian equa-
ν
ν
to measure the capacity of the battery.
• No need for overcharging for cell equalization; hydrogen explosion
hazard is eliminated
RT
nF
a
a
O
O
tion
E E
=
+
ln
0
R
R
The vanadium flow technology is still in its infancy. For it to become a more
viable power storage solution, three requirements must be met: (1) devel-
oping a way to dissolve more V
5+
into the electrolyte solution; (2) finding a
replacement for the membrane—the flow battery's most expensive compo-
nent; (3) achieving greater electrolytic energy density. Stabilizing a future
national grid that draws most of its power from renewable sources may seem
like a tall order for a technology that delivers megawatts, not gigawatts, of
power, but one must remember that this technology is still in its infancy and
as it matures many of its limitations will be solved.
Lithium Ion Batteries
Until the lithium ion (Li-ion) battery was introduced in the early 1990s
nickel-metal hydride batteries were the industry standards for portable
electronic devices. Since their introduction, Li-ion batteries have made sig-
nificant strides in weight, capacity, and power, compared to their nickel-
metal hydride competitors. Li-ion batteries are used extensively in consumer
electronics, but their use in larger scale applications such as electric vehicles
has been limited to date. The primary reasons for the delayed deployment
are safety and high cost; and both issues are related. Although costs can be
reduced with economies of scale of larger batteries, larger batteries are more
difficult to cool and thus more prone to heat gain and the effects of high
temperatures.
Ten years before the introduction of Li-ion batteries, the development
of new hydride materials for nickel-metal batteries achieved a 30 to 40%
increase in energy density compared to their nickel-cadmium predecessors.
This was a quantum leap in battery technology and served to make nickel-
metal-hydride the leader for use in portable electronics.
However, a number of issues surround nickel-metal hydride batteries:
limited discharge currents, high levels self-discharging, long recharge times,
and heating during recharging. The introduction of Li-ion batteries seemed
to solve a number of issues inherent in nickel-based technology.
10
Li-ion
