Li-S batteries function by taking advantage of capillary forces

By Jean-Jacques
DeLisle, contributing writer

 

Battery
technology is a fast-growing and ever-changing field, and new advancements are
produced every day. Until recently, lithium-ion batteries have had a monopoly
on the rechargeable battery market, but their time may be near an end now that
new lithium-sulfur batteries are becoming more viable. Thanks to some
interesting new advancements in energy storage, the sulfur-based batteries are
quickly matching, and in some ways exceeding, their lithium-ion counterparts.
Let us dive into the mechanics of how these new batteries work and what it
means for us and the future of energy itself.

 

In
the lab of Professor Do Kyung Kim, who comes from the KAIST Department of
Materials Science, a new type of battery has been engineered. Enter the new high-areal-capacity lithium-sulfur batteries (Li-S
batteries), which are at the cutting edge of design for energy storage. Li-S
batteries function by taking advantage of capillary forces, and by entangling
polysulfide molecules with carbon nanofibers, researchers have managed to
overcome some of the previous problems with older models. As technology
advances, the need to store massive amounts of energy in a portable and
convenient way is becoming more and more critical. Sulfur-based batteries could
be a solution to this problem but traditional Li-S batteries still have a few
quirks that need to be worked out. Scientists have had to overcome many hurdles
to bring Li-S batteries to the market, including the low electrical
conductivity of sulfur, volumetric expansion and contraction of the battery
while charging or discharging, and permanent damage of the electrode caused by
the dissolution of the lithium-polysulfide into the electrolyte, a problem known
as the “shuttle effect.” 

Image source:
KAIST.

 

To
overcome the obstacles facing Li-S batteries, researchers and scientists have
had some success trying several different methods. One method was to coat the
sulfur with metal oxides, or carbonaceous matrices that make use of
zero-dimensional (OD) carbon materials. The use of these materials resulted in
an increase in conductivity and a reduction of some of the thermal expansion
that came from charging. Do Kyung Kim’s team built upon this innovation and
began using one dimensional (1D) carbon materials. 1D carbon materials have an
advantage over 0D matrixes, as their larger surface area allows them to conduct
more electrons and provide more current at a lower contact point resistance.

 

This
development was made by exploiting the natural force of capillary action. In
order to develop these new batteries researchers had to overcome the high
energy associated with the dissolution of polysulfides. To do this they used
carbon nanofibers, that when soaked in polysulfides, use capillary action to
suppress the dissolution of the sulfides and provide a high level of electrical
conductivity. This winning combination allows the sulfur contained per unit
area (mg/cm2) to be five times greater than the previous battery models that
have been produced. 

These
new lithium-sulfur batteries contain an aerial capacity of 7 mAh/cm2, which
amounts to up to seven times that of a conventional lithium-ion battery. That
means that very soon we can expect to see lithium-ion batteries falling out to
the wayside and sulfur-based carbon-fiber mesh batteries taking over. “This
study brought us closer to commercial-grade high-capacity Li-S batteries, which
are applicable for a wide variety of products, including electric vehicles,
unmanned aerial vehicles (UAVs), and drones,” said Professor Kim.

 

Many
industries will be affected by the rise of lithium-sulfur batteries. In fact, everything
from electric cars and solar energy storage to smartphones and computers will
be affected. With such an increase in capacity from lithium-ion batteries
there’s no reason why we shouldn’t be seeing sulfur make its way technological
applications both industrial and domestic. According to a senior market analyst
at Technavio, a company that specializes in market trends and analysis, the
global lithium-sulfur battery market will grow at a CAGR of over 71% over the
next ten years or so. This rampant growth is not only fueled by the batteries
desirable features but stringent laws against lead pollution have lead
fabricators to look for more environmentally friendly ways to produce
batteries.

 

Older
less efficient lead-acid batteries produce large amounts of waste both in
production and when disposed. Though recycling can mitigate some of this waste,
the older batteries contain large amounts of sulfuric acid, which absorbs some
of the lead during discharge and cannot be easily recycled or disposed of.
Lithium sulfur batteries by using sulfur instead of lead do not require the use
of sulfuric acid of other more harmful chemicals and allow for them to be
disposed easily, or recycled. The production of Li-S batteries is much cleaner
and less wasteful than previous battery types, which explains its allure to
manufacturers as more and more businesses attempt to become more
environmentally conscious.

 

Though
sulfur batteries will no doubt find many applications in the future, the
largest market for them is definitely aviation, when drones and electric
aircraft are being produced faster than ever, driving up the demand for
powerful batteries. The automotive industry is also a key player, and with more
and more electric vehicles on the road every day the automotive industry should
account for 5% of the total market by 2022.

 

Lithium
sulfur batteries are set to revolutionize the world of energy storage in the coming
years in ways that we can only imagine. With the new batteries massive increase
in storage capacity we can expect to see electric cars and drones that can
travel at ever increasing distances on a single charge. Handheld technology
such as smartphones and other gadgets will also receive a substantial boost in
battery life, and with sulfur being a relatively inexpensive material,
production costs should go down.  Solar
energy production is growing each year and with it is the demand for long
lasting batteries with large storage capacities, another niche that LI-S
batteries could easily fill.

 

The
new sodium batteries have many advantages over traditional lithium-ion or lead
acid batteries and will be replacing them in the future in many applications. As
we say goodbye to the energy storage systems of the past and usher in the new
sulfur batteries, we enter into a new age technology: cleaner energy being
created and cleaner processes being used to create batteries to store that
energy. The future is looking brighter than ever, and those lights are powered
by sulfur.