Is Lithium-ion safe?
battery recall raises concerns
By Isidor Buchmann
Cadex Electronics Inc.
www.buchmann.ca - www.BatteryUniversity.com
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 1970's 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 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
current will flow between the positive and negative plates.
This causes the temperature to rise, leading to a thermal
runaway, also referred to 'venting with flame.'
Lithium-ion cells with cobalt cathodes (same as the recalled
laptop batteries) should never rise above 130°C (265°F).
At 150°C (302°F) the cell becomes thermally unstable,
a condition that can lead to a thermal runaway in which flaming
gases are vented.
During a thermal runaway, the high heat of the failing cell
can propagate to the next cell, causing it to become thermally
unstable as well. In some cases, a chain reaction occurs in
which each cell disintegrates at its own timetable. A pack
can get destroyed within a few short seconds or linger on
for several hours as each cell is consumed one-by-one. To
increase safety, packs are fitted with dividers to protect
the failing cell from spreading to neighboring cells.
level of lithium-ion systems
There are two basic types of lithium-ion chemistries: cobalt
and manganese (spinel). To achieve maximum runtime, cell phones,
digital cameras and laptops use cobalt-based lithium-ion.
Manganese is the newer of the two chemistries and offers superior
thermal stability. It can sustain temperatures of up to 250°C
(482°F) before becoming unstable. In addition, manganese
has a very low internal resistance and can deliver high current
on demand. Increasingly, these batteries are used for power
tools and medical devices. Hybrid and electric vehicles will
The drawback of spinel is lower energy density. Typically,
a cell made of a pure manganese cathode provides only about
half the capacity of cobalt. Cell phone and laptop users would
not be happy if their batteries quit halfway through the expected
runtime. Rather than less, the consumer wants more stored
energy to support new features that chew up extra battery
To find a workable compromise between high energy density,
operational safety and good current delivery, manufacturers
of lithium-ion batteries use different cathode metals. Typical
mixes are cobalt, nickel, manganese and iron phosphate. Lithium-ion
systems are not yet mature and have the potential of increasing
the energy density further. Looking back in history, lithium-ion
has achieved a notable energy improvement of 8-10% per annum.
Packing more energy into a cell increases safety concerns
and appropriate measures will need to be taken to achieve
the mandated safety standard set forth by UL 1642. Whereas
a nail penetration test could be tolerated on the older 1.35Ah
18650 cell, a high-density 2.4Ah would become a bomb when
performing the same test. UL 1642 does not require nail penetration.
safety comes First
Let me assure the reader that lithium-ion batteries are safe
and heat related failures are rare. The battery manufacturers
achieve this high reliability by adding three layers of protection.
They are:  limiting the amount of active material to achieve
a workable equilibrium of energy density and safety;  inclusion
of various safety mechanisms within the cell; and  the
addition of an electronic protection circuit in the battery
These protection devices work in the following ways: The PTC
device built into the cell acts as a protection to inhibit
high current surges; the circuit interrupt device (CID) opens
the electrical path if an excessively high charge voltage
raises the internal cell pressure to 10 Bar (150 psi); and
the safety vent allows a controlled release of gas in the
event of a rapid increase in cell pressure. In addition to
the mechanical safeguards, the electronic protection circuit
external to the cells opens a solid-state switch if the charge
voltage of any cell reaches 4.30V. A fuse cuts the current
flow if the skin temperature of the cell approaches 90°C
(194°F). To prevent the battery from over-discharging,
the control circuit cuts off the current path at about 2.50V/cell.
In some applications, the higher inherent safety of the spinel
system permits the exclusion of the electric circuit. In such
a case, the battery relies wholly on the protection devices
that are built into the cell.
We need to keep in mind that these safety precautions are
only effective if the mode of operation comes from the outside,
such as with an electrical short or a faulty charger. Under
normal circumstances, a lithium-ion battery will simply power
down when a short circuit occurs. If, however, a defect is
inherent to the electrochemical cell, such as in contamination
caused by microscopic metal particles, this anomaly will go
undetected. Nor can the safety circuit stop the disintegration
once the cell is in thermal runaway mode. Nothing can stop
it once triggered.
A major concern arises if static electricity or a faulty charger
has destroyed the battery's protection circuit. Such damage
can permanently fuse the solid-state switches in an ON position
without the user knowing. A battery with a faulty protection
circuit may function normally but does not provide protection
Another safety issue is cold temperature charging. Consumer
grade lithium-ion batteries cannot be charged below 0°C
(32°F). Although the packs appear to be charging normally,
plating of metallic lithium occurs on the anode while on a
sub-freezing charge. The plating is permanent and cannot be
removed. If done repeatedly, such damage can compromise the
safety of the pack. The battery will become more vulnerable
to failure if subjected to impact, crush or high rate charging.
Asia produces many non-brand replacement batteries that are
popular with cell phone users because of low price. Many of
these batteries don't provide the same high safety standard
as the main brand equivalent. A wise shopper spends a little
more and replaces the battery with an approved model.
Figure 1 shows a cell phone that was destroyed while charging
in a car. The owner believes that a no-name pack caused the
1: A cell phone with a no-brand battery that vented with
flame while charging in the back of a car.
the infiltration of unsafe packs on the market, most manufacturers
sell lithium-ion cells only to approved battery pack assemblers.
The inclusion of an approved safety circuit is part of the
purchasing requirement. This makes it difficult for a hobbyist
to purchase single lithium-ion cells off-the-shelf in a store.
The hobbyist will have no other choice than to revert to nickel-based
batteries. I would caution against using an unidentified lithium-ion
battery from an Asian source, if such cells is available.
The safety precaution is especially critical on larger batteries,
such as laptop packs. The hazard is so much greater than on
a small cell phone battery if something goes wrong. For this
reason, many laptop manufacturers secure their batteries with
a secret code that only the matching computer can access.
This prevents non-brand-name batteries from flooding the market.
The drawback is a higher price for the replacement battery.
Readers of www.BatteryUniversity.com
often ask me for a source of cheap laptop batteries. I have
to disappoint the shoppers by directing them to the original
vendor for a brand name pack.
Considering the number of lithium-ion batteries used on the
market, this energy storage system has caused little harm
in terms of damage and personal injury. In spite of the good
record, its safety is a hot topic that gets high media attention,
even on a minor mishap. This caution is good for the consumer
because we will be assured that this popular energy storage
device is safe. After the recall of Dell and Apple laptop
batteries, cell manufacturers will not only try packing more
energy into the pack but will attempt to make it more bulletproof.
About the Author
Isidor Buchmann is the founder and CEO of Cadex Electronics
Inc., in Vancouver BC. He has studied the behavior of rechargeable
batteries in practical, everyday applications for two decades.
Award winning author of many articles and books on batteries,
Mr. Buchmann has delivered technical papers around the world.
Isidor Buchmann is the founder and CEO of Cadex Electronics
Inc., in Vancouver Canada. Founded in 1980, Cadex specializes
in the design and manufacturing of advanced battery charging
and testing instruments. For product information please visit