Areal capacity of Li-S batteries is up to seven times that of conventional Li-ion

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 (Li-S)
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.

 

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, 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.

 

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:
NXP.

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. This
means that very soon we can expect to see lithium-ion batteries falling 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, from electric cars and
solar energy storage to smartphones and computers. With such an increase in
capacity from lithium-ion batteries there’s no reason why we shouldn’t see
sulfur make its way into consumer and industrial applications. 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 compound annual
growth rate (CAGR) over 71 percent in the next ten years or so. This rampant
growth is not only fueled by the batteries’ desirable features, but also
stringent laws against lead pollution, which have led fabricators to look for
more environmentally-friendly ways to produce batteries.

 

Older
less efficient lead-acid batteries produce a large amount 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 disposed of or recycled. Li-S
batteries by using sulfur instead of lead do not require the use of sulfuric
acid or other more harmful chemicals, which allows them to be disposed of
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 clearly aviation, where 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 percent of the total market by 2022, according to the Technavio report.

 

Li-S
batteries are set to revolutionize the world of energy storage in the coming years.
With the new battery’s 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.