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With Tesla’s battery day event not too far
off, and their acquisition of Maxwell Technologies
last year, I thought it was worth taking a
closer look at supercapacitors. Some believe
that supercapacitors might be integrated into
future EVs. But, what exactly is a supercapacitor?
And what makes them so different from batteries?
Are they really the future of energy storage?
I'm Matt Ferrell ... welcome to Undecided.
Before we get into the nitty gritty of whether
supercapacitors can really change energy storage
all on their own, it’s worth taking a look
at what they are and how they’re different
from something like a lithium ion battery.
Both batteries and capacitors are a method
of storing energy, but Lithium-Ion batteries
rely on chemical reactions to store and release
their energy. It’s made up of a positive
and negative side, which are called the cathode
and anode. Those two sides are submerged in
a liquid electrolyte and are separated by
a micro perforated separator, which only allows
ions to pass through. When the battery charges
and discharges, the ions flow back and forth
between the cathode and anode. During this
process the battery is heating up, expanding
and contracting. These reactions degrade the
battery over time, giving batteries a limited
lifespan. One benefit of battery technology
is a very high specific energy, or energy
density, so it can store a lot of energy for
later use.
But capacitors are different, they don't rely
on chemical play in order to function. Instead,
they store potential energy electrostatically.
Capacitors use a dielectric, or insulator,
between their plates to separate the collection
of positive and negative charges building
on each plate. It's this separation that allows
the device to store energy and quickly release
it. It’s basically capturing static electricity.
One benefit of this is that a 3V capacitor
now will still be a 3V capacitor in 15-20
years time. While a battery may lose voltage
capacity over time and use. And unlike a battery,
a capacitor has a much higher power throughput,
so it can charge and discharge in a fraction
of the time ... but they have a very low specific
energy. It’s good for very small bursts
of power.
And that’s where supercapacitors enter the
scene. They start to bridge the gap between
a battery and capacitor. The concept of a
"supercapacitor" is not a new thing. In fact,
in 1957 the first supercapacitor device was
created by General Electric, but there aren’t
any known commercial applications. In 1966,
Standard Oil accidentally discovered the double-layer
capacitor when working on fuel cells, but
it wasn’t until the late 1970’s that the
Japanese company, NEC, began commercially
offering the first "supercapacitor" for computer
memory backup. In fact, while we commonly
refer to many products as "supercapacitors"
or “ultracapacitors,” those two terms
are used interchangeably and really depends
on what the company producing it wants to
call it. For the most part it’s really just
a trademark thing.
In the 1990's, products such as ECOND's PSCap
-- a starter for diesel trains -- began hitting
the market and pushing the boundaries of energy
storage and capacitor applications. Companies
like Maxwell Technologies, Murata and Tecate
generally dominate the supercapacitor field.
But recent developments in graphene-based
capacitors are once again nurturing the growth
of supercapacitor efficiency and application
... but I'll talk more about that a bit later.
First we need to talk about how a supercapacitor
works? And how it’s different than a regular
capacitor? Because it’s kind of cool ... it’s
starting to venture towards a battery’s
design and use an electrolyte on either side
of an insulator. When current is applied ions
build up on either side of the insulator and
create a double-layer of charge.
What makes a supercapacitor truly superior
to a normal capacitor, or even a battery,
is the distance between the metal plates.
In a normal capacitor the distance is around
10-100 microns (a micron is one-thousandth
of a millimeter). But in a supercapacitor
that distance is narrowed to one-thousandth
of a micron, and that smaller distance leads
to a larger electric field -- i.e. more energy
storage. Not too mention, the carbon coated
plates on supercapacitors increase the available
surface area for storage capacity by up to
100,000 times. That's a lot more energy available
for use than a normal capacitor.
So, what are these power hungry little titans
used for?
We're really just at the beginning of supercapacitor
applications. But, in general, they've been
found to have the biggest potential for application
in hybrid-transportation (cue the Tesla/Maxwell
speculation here). Toyota, Peugeot-Citroen,
Mazda and even Lamborghini have all released
models of vehicles that use some combination
of supercapacitors and conventional Li-Ion
batteries. Believe it or not, even though
Tesla invested $200 million in the purchase
of Maxwell Technologies, Elon Musk has said
his focus is not on expanding the use and
development of Maxwell's supercapacitors for
Tesla vehicles but instead in their battery
manufacturing technology. However cars like
Toyota's Hybrid-R concept car and Lamborghini's
high powered Sian are using supercapacitors
for a very specific role: Power regeneration
systems during deceleration.
In other words, when cars are slowing, the
energy generated from that action is stored
by supercapacitors onboard and later used
for acceleration -- saving batteries for less
strenuous actions than acceleration and deceleration.
It’s taking advantage of a supercapacitors
superior power throughput.
A fantastic example of how effective supercapacitors
can be is seen in Switzerland where a fleet
of buses will be exposed to charging stations
at a variety of stops along their route. Just
15 seconds can top the energy charge off and
only a few minutes would suffice for a full
charge. With frequent top offs it makes up
for the lack of energy density and storage.
And because supercapacitors draw a lower current
over a period of a few minutes at a time,
this puts less stress on the grid.
However, supercapacitors still can't compete
with Li-ion batteries when it comes to that
high specific energy and longterm energy storage.
But despite that some companies are making
progress on projects that are poised to make
supercapacitors more universally applicable.
You may have watched my recent videos on graphene
and carbon nanotubes. Well, those materials
actually play a role in the future of supercapacitors.
Companies like NAWA Technologies and Skeleton
Technologies have taken supercapacitors to
the next level by incorporating graphene into
the coating of the metal plates. They've taken
this and expanded the conventional use of
supercaps into markets like components for
e-motorcycles, spacecrafts and wave energy
technology.
Graphene provides the next generation of supercapacitors
with an interesting array of improvements.
In particular, graphene offers substantially
more surface area, giving supercapacitors
even *more* capacity for energy storage. But
in addition to that, graphene is ultralight,
has unique elasticity and is incredibly strong.
In fact, NAWA Technologies, Skeleton and other
supercapacitor/battery companies have already
found major applications for their graphene-based
supercapacitors. Skeleton's products can be
found helping to power major tram-systems
in big European hubs like Warsaw and Mannheim.
But it's not just trams and urban transportation
that Skeleton has found use for. They're working
with the European Space Agency on a potential
approach for sudden power usage on satellites
and spacecraft. As well as developing an ultracapacitor
module for use in wind turbines to help manage
the blade pitch control.
NAWA's "NAWA Racer", an e-motorcycle that
packs a serious punch, is showing the world
what ultracap-Li-ion hybrid power systems
can do in smaller vehicles by making this
bike incredibly efficient. While the bike
itself isn't being rolled out for commercialized
sale, what it's doing is proving to other
companies interested in the potential of supercapacitor/Li-ion
setups, that the technology is groundbreaking.
The bottleneck in absorbing all of the regenerative
breaking power is the battery, which has a
very slow charge rate. The supercapacitor
combo allows it to recoup 80-90% of the energy
from braking and then immediately reuse that
for acceleration.
But wait ... there's more! Eaton's supercapacitors
are built to pair with battery systems, Dongxu
Optoelectronics fast charging laptop battery
system, Earthdas supercap/battery mixture
for e-bikes and motorcycles and ZapGo's e-scooters
are all examples of small power management
companies that are experimenting with the
application of supercapacitors in their technology.
With all these examples, there doesn't seem
to be any mass movement towards the replacement
of batteries with supercapacitors in everyday
technology. So, why is that?
Well, the short answer is that supercapacitors,
while superior to traditional capacitors in
their ability to store and release energy,
are still not able to replace the function
of conventional Li-Ion batteries. Mainly because
Li-ion batteries pack a punch that supercapacitors
can't, in the form of specific energy, or
energy density (Li-ion ~250Wh/kg vs. Ultracaps
~20Wh/kg). But even companies that focus on
supercapacitor technology, like Skeleton Technologies,
admit that a hybridization of Li-ion and supercapacitor
driven power systems could propel electric
technologies into the next era. And the reality
is that most of the applications we see today,
are some sort of combination between the two.
When a supercapacitor is placed in parallel
with a traditional battery, we see drastic
changes in the battery lifespan. The process
essentially works like this: the presence
of a supercapacitor in parallel with a regular
battery basically just reduces the work load
and intensity level that the battery has to
endure. Giving the battery more longevity.
In some research it’s shown that it can
extend the life of a battery by up to four
times. So why aren’t we seeing this in all
EVs? Well, battery technology in EVs is currently
good enough, and getting better, for how we’re
using it. The expense for going down this
path may not be worth the investment.
For a technology that is nearly 65 years old,
supercapacitors have yet to really find their
place in electric technology. But it seems
that, in unison with Li-ion batteries and
with graphene being applied more and more
commonly, supercapacitors are slowly building
themselves an important role in hybrid-electric
technology. And that's something that's easy
to overlook -- the importance of streamlining
and improving efficiency of current technologies
by adding, not replacing, a component to the
mix. Supercapacitors could play that role,
making Lithium-ion batteries, which have high
energy density, more useful over longer and
longer periods of time.
The potential is there for supercapacitors
to take charge of the energy-storage game
and redefine what energy storage really is.
We still have a ways to go, but it will be
very interesting to see how they’re applied,
not just to electric cars, buses and other
transportation, but to renewable energy and
the grid as well.
And if you’d like to dive a little deeper
on the underlying principles of supercapacitors,
like static charge and how protons and electrons
move, attract and repel each other, check
out the Electricity and Magnetism course at
Brilliant. This has been one of my favorite
courses so far.
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about magnetism (see what I did there), they
have over 60 courses including topics in computer
science, physics, and mathematics.
They teach all of the concepts through fun
and interactive challenges, which help you
understand the "why" of something ... not
just the "how." This has really tapped into
the way I learn. It helps to develop your
intuition and is my favorite part of Brilliant.
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