of the reason that lithium-ion
batteries are so popular in everything from cellular phones
to automobiles is
their relatively quick charge times, reasonable capacity, and
resistance to fatigue. Unfortunately, Li-ion batteries are still
somewhat expensive as their manufacturing process requires a good
amount of energy and some of their usual metal companions, such as
cobalt and nickel, are not entirely inexpensive.
at the Pacific Northwest National Laboratory (PNNL) with help from
the U.S. Department of Energy are working on developing Li-ion
batteries which can perform at similar levels, but cost much less to
produce. The cost reduction will come from a change in both
production methods and materials used.
than the typical lithium metal oxide construction, the PNNL team
looked to materials to replace the oxide and expensive cobalt or
nickel with a phosphate and manganese or iron. Lithium metal
phosphate batteries are not unheard of, but the PNNL team wanted
something without such complicated production methods and high costs.
scientist at PNNL, Daiwon Choi speaks of the team's technique in
news release, "This method is a lot simpler than other ways
of making lithium manganese phosphate cathodes. Other groups have a
complicated, multi-step process. We mix all the components and heat
simpler process he spoke of involves nothing much more than paraffin
wax and oleic acid (soap), and heat. They began by mixing the
lithium, phosphate, and manganese together with melted wax and oleic
acid. Paraffin wax is made of long and mostly inert molecule chains
which helped direct the crystal growth, while the oleic acid, as a
surfactant, helped spread the important constituents evenly.
they raised the temperature of the mixture. By 400 degrees Celsius,
the wax and soap had evaporated away from the mixture, leaving tiny
lithium manganese phosphate (LMP) crystals of approximately 50 by
2000 by 2000 nanometers. For comparison, a human hair is about 50,000
to 60,000 nanometers in diameter. They further raised the temperature
to bond the crystals together and form a plate of cathode material.
theory, LMP should be rather competitive with typical Li-ion metal
oxide batteries, with a capacitance of about 170 milliAmp hours in
one gram of material. In past tests, researchers had been able to get
up to 120 milliAmp hours with lithium metal phosphate-based
batteries. Choi and colleagues where able to get 168 milliAmp hours
per gram of material in their best case charge/discharge tests. But
the number dipped as low as 54 milliAmp hours during a fast/fast
"real world" test cycle.
numbers are far from disappointing for PNNL. The team was able to
engineer a way to create LMP crystals with simplicity and without
high cost. The work may pave the way for other alternative
lithium-based composite batteries. They also plan further work in
refinement of the carbon backing used as the positive electrode for
the LMP crystal plates.