Dave DeMuro
Motorola Energy Systems Group
Lithium-ion batteries
made their first appearance in the early 1990s, providing higher energy
density for cell phones, albeit at a significant cost premium over nickel
cadmium and nickel metal hydride batteries. Back then there was one supplier
of the technology, essentially one formulation of the chemistry and one
cylindrical form factor for cells. The situation is vastly different today.
A large number of suppliers provide a multitude of form factors for various
energy markets, and new variations of chemical formulations are creating
new markets for lithium-ion batteries. Cell prices have also dropped dramatically
in recent years, opening up markets in low-end consumer electronics.
While lithium-ion batteries have been nearly universally adopted for cell
phones and notebook computers, the two largest portable device markets,
there are certain applications that have posed technical and/or market
challenges which are only now being overcome by lithium-ion batteries.
One such market is cordless power tools. These devices require a large
amount of peak current, and previous versions of lithium-ion cells could
not deliver sufficient current without sustaining damage to the cells,
or posing a safety risk to the user. We are now seeing high current formulations
of lithium-ion cells, which sacrifice some energy density over conventional
cells, being applied to the power tool market.
Another factor that has limited the use of lithium-ion cells in high current
applications like power tools is the safety circuit. Most lithium-ion
battery packs contain over-voltage and under-voltage monitoring circuits
which control solid-state switches in series with the battery terminals.
Scaling up these safety circuits for higher currents can drive up the
cost beyond practical limits, so these higher current applications require
cells that can remain safe in the absence of a conventional safety circuit.
Cells like this are now available, and although they do sacrifice energy
density to achieve the added level of safety, the reduction in system
complexity is making this type of cell attractive even in conventional
applications like cell phones.
Another emerging application for lithium-ion batteries is backup power.
While these batteries are similar in design to those used in notebook
computers, the need for long service life and conditions of continuous
charging pose some unique technical challenges. This is especially true
when using cells from lower cost cell suppliers who employ more manual
assembly processes that result in variation in properties from cell to
cell. It is important for the pack designer to be aware of the performance
capabilities of the cells and design the safety and monitoring circuits
accordingly.
Energy systems are a key enabling technology for electric vehicles, both
large and small. If the low weight and high energy density of lithium-ion
could be applied to electric vehicles, it could cause the market for electric
vehicles to take off. Even small electric vehicles such as scooters or
golf carts require vast amounts of energy storage. In order for the system
to be cost effective, the number of cells used must not be too large,
so the cells themselves need to provide tens or preferably hundreds of
amp-hours of capacity. Lithium-ion cells can be scaled up this size but
more work needs to be done on the thermal and safety side before these
types of systems become mainstream.
Lithium-ion cells and systems continue to evolve rapidly, with new suppliers,
form factors and chemical variations being released. This evolution will
enable lithium-ion to displace existing chemistries in certain markets.
In addition, as technical challenges with scaling up the technology are
overcome, lithium-ion cells will be the enabler for a whole new class
of products.
Contact Motorola at www.motorola.com
Dave DeMuro is
manager of Advanced Development and Platform Design at Motorola Energy
Systems Group. His responsibilities include managing strategic technology
and developing advanced product concepts. Since joining Motorola 19 years
ago, he has served the company in a number of engineering and management
positions of increasing responsibility.
Dave holds a bachelor's
in Electrical Engineering from the University of Illinois and a master's
in Business Administration from the Illinois Institute of Technology.
Dave is an associate member of Motorola's Science Advisory Board, and
he holds 15 patents in the areas of RF circuit design, battery charging
and accessory systems design.
