The next frontier in battery technology: Rechargeable lithium
Good energy density and discharge characteristics could make lithium good for
portable products
Research on both lithium-ion and lithium-polymer continues as battery makers
refine yet another technology for the growing rechargeable battery market.st
Nickel-cadmium (NiCd) and nickel-metal-hydride (NiMH) batteries currently
occupy center stage in the portable battery market. In the not-too-distant
future, however, a third battery technology could be in the spotlight:
rechargeable lithium.
Until now, lithium has been used as a primary battery. Now, however, the
growing market for portable products is causing many battery manufacturers to
look at lithium–either in a liquid-ion or a polymer-ion form–as a secondary,
rechargeable battery.
Lithium has several favorable characteristics. For example, with an operating
voltage of 3.6 V per cell, one lithium-ion battery can replace three NiCd or
NiMH cells that operate at 1.2 V each. At the same time, a typical AA-size
lithium cell weighs just 18 g, compared with 26 g for other rechargeable
batteries. Moreover, lithium batteries have better self-discharge
characteristics than other cell chemistries. The table compares some
characteristics of lithium-ion batteries to NiCd and NiMH types.
On the downside, right now lithium is more expensive to produce than the other
batteries. And, its lower current capacity makes it better suited for
low-drain-rate applications.
Sandia National Laboratories (Albuquerque, NM) has signed a cooperative
research and development agreement with AT&T Bell Labs and three
manufacturers–Eveready Battery Co. (St. Louis), Rayovac (Madison, WI), and
Wilson Greatbatch Ltd. (Clarence, NY). The partners plan to develop a carbon
material that can be used as an anode for rechargeable lithium-ion batteries.
According to Sam Levy, a member of Sandia's technical staff, this development
should help alleviate lithium's energy density and cycle life limitations.
While most rechargeable lithium battery work revolves around liquid ion, some
work has been done on lithium polymer. Gould Electronics (Eastlake, OH) is
researching lithium polymer, and Energizer Power Systems (Gainesville, FL)
recently announced a joint agreement with Valence Technology (San Jose, CA) to
develop lithium polymer batteries.
Lithium polymer uses a conducting polymer film that acts both as a separator
and electrolyte. It differs from lithium-ion in that it is more of a “dry”
chemistry and does not require a robust casing to contain the wet electrolyte.
According to Anthony Wong, director of marketing for Gould, lithium polymer
does not charge and discharge as quickly as lithium-ion. However, the battery
is potentially less expensive to manufacture because a less robust battery
casing can be used. Wong suggests that the applications for lithium polymer
batteries will be those requiring low battery drain.
Another company researching lithium polymer is Hope Technologies (Willow Grove,
PA). Hope is developing a lithium polymer battery, called the Lithion, that
reportedly produces six times the energy of a lead-acid battery and four times
the energy of a nickel-cadmium battery having the same weight. According to the
company, the Lithion can potentially last four times longer than a conventional
laptop battery.
The Lithion battery has good discharge characteristics. It has a monthly
self-discharge rate of just 1%, and is capable of 150 deep discharge cycles
without physical deterioration. The battery can be made in any shape or size.
Even if the technical issues surrounding rechargeable lithium batteries get
ironed out, don't expect widespread availability of lithium-ion or
lithium-polymer batteries anytime soon. Ritch Russ of Maxell Corp.of America
(Fair Lawn, NJ) estimates that production quantities of rechargeable lithiums
will not be available in the United States for at least a year. “As with NiMH
batteries which are just now becoming widespread, battery makers want to test
market rechargeable lithiums to key OEMs first so any possible flaws are
resolved,” says Russ. For its part, Maxell is starting to test market
lithium-ion batteries through Hitachi. It will be a while before they will be
widely available in the U.S.
Japan-based companies appear to be in the lead in producing rechargeable
lithiums. Sanyo has announced its plans to market in the U.S.a rechargeable
cylindrical lithium that uses a patented graphite cathode. It is rated 3.6 V
per cell and can charge in 1 1/2 hours. The company is also developing a line
of compatible chargers for the batteries. Sampling of these lithium batteries
is just beginning, according to Joe Carcone, Sanyo's vice president of sales
and marketing.
Moli Energy (Vancouver, British Columbia, Canada) is also readying a
lithium-ion battery, under the Molicel name. The first product, designated the
Model ICR-18650, is a coin-cell-type battery measuring 18 mm in diameter. It is
rated 1,200 mAh at 3.7 V and can charge in two to four hours. Discharge
capacity is 2,400 mA. Manufacturing of the batteries begins this month. Moli
plans to bring out other lithium-ion batteries in both cylindrical and
prismatic configurations.
Other companies researching and/or developing rechargeable lithium batteries
include Panasonic Industrial Co. (Secaucus, NJ), Saft America (Valdosta, GA),
Renata Batteries (Richardson, TX), Duracell (Bethel, CT), and Tadiran (Port
Washington, NY).
–Spencer Chin
TABLE:
Comparison of AA Cells
Feature NiCd NiMH Li Ion
——————————————————–
Capacity (mAh) 660 1,300 400
Working voltage
(V) 1.2 1.2 3.5
Discharge power
(mWh) 780 1,660 1,440
Weight (g) 26 26 18
Volume (cm 3) 8.3 8.3 8.3
Energy density
(mAh/cm 3) 78 157 48
Maximum current
(A) 5 3 1
Usable low
temperature ( C) -20 0 0
Quick charge
(minutes) 15 60 60
Charge method Constant Trickle, Constant current
current, constant and constant
floating voltage voltage
Applications Low price Medium price Small
Big current Big and medium Light weight
price Medium current
Long-term use
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