Nanotechnology Improves Lithium-ion Batteries
By
Michael Campbell
ENGR 1050 Introduction to Nanotechnology, Summer 2015
As energy becomes more and more scarce through depleteable resources, energy
storage will become more important. Batteries have become the staple for energy storage and
while earlier forms of batteries have served their purpose (and continue to be of some value),
lithium batteries have emerged as the leader of secondary (or rechargeable) batteries. The
questions now are what materials work best with lithium and how can the materials be
arranged to optimize the battery’s performance?
As a brief introduction, batteries
are composed of three components: (1) a
negative electrode called an anode, (2) a
positive electrode called a cathode, and
(3) an electrolyte solution between the
anode and the cathode. Lithium has been
found to be ideal for the internal
components of rechargeable batteries
because it is the lightest metal, it has the
greatest electrochemical potential, and it
Figure 1 Typical Battery
has the largest specific energy per weight. One additional advantage of lithium is described by
Armand and Tarascon in their February 2008 article printed in Nature:
The stored energy content of a battery can be maximized in three ways: (1) by
having a large chemical potential difference between the two electrodes; (2) by
making the mass (or volume) of the reactants per exchanged electron as small as
possible; and (3) by ensuring that the electrolyte is not consumed in the
2
chemistry of the battery. This final condition was not true of the three principal
battery technologies developed in the twentieth century, but holds for …
lithium-ion batteries (Armand & Tarascon, 2008).
Much research is now underway to discover the best materials to combine with lithium in order
to maximize its performance and reduce safety risks. Nanotechnology has made it possible to
explore these materials and develop better, more efficient batteries.
One issue that lithium batteries with metal electrodes experience is a relatively large
volume expansion and contraction during charge and discharge. To combat this issue, Jusef
Hassoun et al. from the University of Rome attempted to develop a method of introducing a
reduced particle size of the anode material (to the order of nanodimensions) in order to reduce
the volume expansion and contraction of the material (Hassoun, Reale, Panero, & Scrosati,
2008). Their report established that this common approach of reducing the particle size of the
metal components to a nanodimension was only successful upon limiting the cycling regime to
a fraction of the total capacity, which is not very practical.
Tom Lecklider explores in his June 2008 article printed at www.evaluationengineering.com the
idea of replacing the typical metal oxide cathode found in most lithium batteries with ironphosphate nanoparticles that have been coated with carbon (Lecklider, 2008). The ironphosphate properties virtually eliminate thermal runaway due to stronger oxygen bonds than
metal oxide cathodes. Because the iron-phosphate cathodes maintain their size while
charging/discharging, as opposed to metal oxide cathodes which expand or contract, the
3
batteries can withstand at least twice as many charge/discharge cycles. The carbon surrounding
the iron-phosphate nanoparticles increases the energy density significantly.
In the same article, Lecklider describes another nanotechnology that replaces the typical
carbon anode with a lithium titanate material which has similar benefits to the iron-phosphate
cathode. The lithium titanate maintain their size during the charging/discharging cycles,
increasing the batteries lifespan. The lithium titanate material, when produced at a nanoscale,
does not react with the electrolyte in the battery to create a solid electrolyte interface (SEI).
This is significant for a few reasons. First, SEI limits the charging and discharging rates of the
battery. Second, SEI breaks down at temperatures greater than 120°C and become virtually
nonconductive below 0°C, both of which create a condition for thermal runaway. Finally, SEI
limits the voltage window of the battery from 2.0 V to 4.2 V. With a lithium titanate anode that
does not produce SEI, a battery can be charged to 90% in thirty minutes at -30°C, increase the
charge/discharge cycles by at least a factor of ten, and increase the voltage window from 0 V to
about 5 V over a temperature
range from -50°C to 260°C.
Another alternative for
the anode has been explored by
Keli
Zhang
of
the
Wuhan
University in Wuhan, China. He
and his colleges found that
molybdenum
disulfide
when
synthesized with an intercalation structure has much better performance than other
Figure 2 SEM Image
of molybdenum disulfide.
4
rechargeable batteries, especially because of its high energy density (Guo, Hong, Cong, Zhou, &
Zhang, 2005). It was observed to contain a first discharge capacity 3.4 times larger than that of
graphite (typical graphite capacity is 330 mAh/g, observed MoS2 capacity was 1272 mAh/g).
Even after the 20th cycle the observed charge capacity was still more than 400 mAh/g. The
molybdenum disulfide powder was synthesized in a hydrothermal manner and the particles of
the powder measured about 200 nm. An X-ray diffraction pattern of the powder indicated the
particles to have a poor crystalline structure.
Figure 5 Pristine Tin Oxide Nanowire
As nanotechnology is introduced into the development of lithium batteries, caution will
need to be taken at every turn. An American Institute of Physics article in 2011 describes how a
new technique of using nanowires as an anode can grow lithium fibers that may short circuit
the battery (Liu, et al., 2011). Their tests included a silicon nanowire immersed in an ionic liquid
electrolyte and a bulk lithium cobalt oxide cathode. Long lithium fibers were found on the tips
of the nanowires after charging. These fibers grew directionally to a length of up to tens of
microns. Also, a lithium fluoride film
was found on the lithium fibers
indicating the decomposition of the
electrolyte. Both of these issues could
contribute
to
battery malfunction
Figure 3 Lithium
crystal on nanowire.
Figure 4 Image series of pull-out process of nanowire from ILE.
5
and even possible safety issues.
So far in the batteries described above, the
electrolyte was lithium in an aqueous solution.
Another option is called an all-solid-state battery,
where the anode, cathode, and electrolyte are
solid. The
challenge
with
Figure 6 Cross sectional SEM image of titanium sulfide film
deposited on a silicon substrate.
this
method is manufacturing materials that have ideal
electrode-electrolyte interfaces. Takuya Matsuyama
et al. used a method called pulsed laser deposition to
prepare an amorphous, thin film of titanium sulfide (a
demonstrated electrode material) on a 400 nm silicon
substrate
Figure 7 High resolution TEM image of titanium sulfide
thin film.
for
use
in
all-solid-state
batteries
(Matsuyama, et al., 2012). Matsuyama achieved a
reversible capacity of 543 mAh/g.
Although our energy reserves from depleteable resources are shrinking and our demand
for energy is increasing, there are great strides being achieved in the storage of energy through
the use of the lithium ion battery. And despite the design and safety issues that have and will
be discovered, nanotechnology is providing the greatest advances in the performance
enhancement of lithium ion batteries.
6
References
Armand, M., & Tarascon, J. -M. (2008). Building Better Batteries. Nature, 652-657.
Guo, G., Hong, J., Cong, C., Zhou, X., & Zhang, K. (2005). Molybdenum Disulfide Synthesized by
Hydrothermal Method as Anode for Lithium Rechargeable Batteries. Journal of Material Science,
2557-2559.
Hassoun, J., Reale, P., Panero, S., & Scrosati, B. (2008). Novel Lithium Ion Batteries Based on a Tin Anode
and on Manganese Oxide Cathodes. Isreal Journal of Chemistry, 229-234.
Lecklider, T. (2008). Nanotechnology Drives Battery Development. Evaluation Engineering, 48-53.
Liu, X. H., Zhong, L., Zhang, L. Q., Kushima, A., Mao, S. X., Li, J., . . . Huang, J. Y. (2011). Lithium Fiber
Growth on the Anode in a Nanowire Lithium Ion Battery during Charging. Applied Physics
Letters.
Matsuyama, T., Sakuda, A., Hayashi, A., Togawa, Y., Mori, S., & Tatsumisago, M. (2012). Preparation of
Amorphous TiSx Thin Film Electrodes by the PLD Method and their Application to All-solid-state
Lithium Secondary Batteries. J Mater Sci, 6601-6606.
7