Is LITHIUM-ION
Safe?
Major Battery Recall Raises Concern
by Isidor Buchmann
When Sony introduced the first
lithium-ion battery in 1991, they
knew of the potential safety risks. A
recall of the previously released
rechargeable metallic lithium battery
was a bleak reminder of the discipline
one must exercise when dealing
with this high energy-dense battery
system.
Pioneering work for the lithium
battery began in 1912 by G. N. Lewis.
It was not until the early 1970s when
the first non-rechargeable lithium batteries became commercially available.
Attempts to develop rechargeable
lithium batteries followed in the
eighties. These early models were
based on metallic lithium and offered
very high energy density.
However, inherent instabilities of
lithium metal, especially during
charging, put a damper on the development. The cell had the potential of
a thermal run-away. The temperature
would quickly rise to the melting point
of the metallic lithium and cause a
violent reaction. A large quantity of
rechargeable lithium batteries sent to
Japan had to be recalled in 1991 after
the pack in a cellular phone released
hot gases and inflicted burns to a
man’s face.
Because of the inherent instability
of lithium metal, research shifted to a
non-metallic lithium battery using lithium ions. Although slightly lower in
energy density, the lithium-ion system
is safe, providing certain precautions
are met when charging and discharging. Today, lithium-ion is one of the
most successful and safe battery
chemistries available. Two billion cells
are produced every year.
Lithium-ion holds twice the
energy of a nickel-based battery and
four-times that of lead acid. Lithium-ion is a low maintenance system, an
advantage that most other chemistries
FIGURE 1. A cell
phone with a no-brand
battery that vented with
flame while charging in
the back of a car.
cannot claim. There is no memory and
the battery does not require
scheduled cycling to prolong its life.
Nor does lithium-ion have the
sulfation problem of lead acid that
occurs when the battery is stored
without periodic topping charge.
Lithium-ion has a low self-discharge
and is environmentally friendly.
Disposal causes minimal harm.
With the high usage of lithium-ion
in cell phones, digital cameras, and
laptops, there are bound to be issues.
A one-in-200,000 failure rate triggered
a recall of almost six million lithium-ion packs used in laptops manufactured by Dell and Apple. Heat-related
battery failures are taken very
seriously and manufacturers chose a
conservative approach. The decision
to replace the batteries puts the
consumer at ease and lawyers at bay.
Let’s now take a look at what’s behind
the recall.
Sony Energy Devices (Sony), the
maker of the lithium-ion cells in
question, says that on rare occasions
microscopic metal particles may
come into contact with other parts of
the battery cell, leading to a short circuit within the cell. Although battery
manufacturers strive to minimize the
presence of metallic particles,
complex assembly techniques make
the elimination of all metallic dust
nearly impossible. Energy dense cells
with ultra-thin separators are more
susceptible to impurities than older
designs with lower Ah ratings.
A mild short will only cause an
elevated self-discharge. Little heat is
generated because the discharging
energy is very low. If, however,
enough microscopic metal particles
converge on one spot, a major electrical short can develop and a sizable
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December 2006
