e031066.pdf

ELECTRONICS ONLINE

The Truth about

Batteries

are Li-Ion batteries really that bad?

By Harry Baggen

Today’s society is marked by an increasing amount of ‘wireless’ equipment.

This trend extends to communications as well as to power supplies for

portable equipment. The best known examples are the laptop computer

and the GSM telephone. Thanks to powerful batteries, such equipment is

capable of working for long periods without mains power. But what about

the quality of the various kinds of batteries, and how long will they last?

NiMH, Li-Ion and Li-polymer (there’s

also the sealed lead-acid battery but

that’s rarely found in modern

portable equipment).

Nickel-Cadmium (NiCd) is the

oldest type. By virtue of its low

internal resistance, it is very suit-

able for applications requiring rela-

tively high currents. Unfortunately

this battery type contains highly

poisonous Cadmium and it should

have disappeared from the Euro-

pean market within a couple of

years. As a replacement the metal-

hydride battery was developed,

whose performance has been

pushed to a level not far from that of

the NiCd battery. Although their

internal resistance is slightly higher,

NiMH batteries may be considered

a perfect replacement for a NiCd

battery in many applications. For

applications in which the energy

density is crucial (i.e., a lot of

energy from a small device), the Li-

Ion battery has been developed.

Unfortunately this suffers from one

big drawback in that it requires a

special charger. A derivate, the

Lithium-polymer battery with a flex-

More and more equipment relies on batter-

ies (rechargeable or not) for the power sup-

ply. In and around the home, non-recharge-

able batteries are used for the central heating

thermostat, torchlight, radio and personal

stereo. Rechargeable batteries are typically

applied in equipment with higher current

consumption, such as digital cameras and

portable computers. The GSM

phone, too, can’t do without a pow-

erful battery because it needs to be

on all day so has to be recharged

from time to time.

As most readers of this magazine

will know, there are several types of

battery around these days: NiCd,

Elektor Electronics

1/2003

ELECTRONICS ONLINE

Internet Addresses:

[1] Digit-life.com:

www.digit-life.com/articles/

mobileaccumulators/

[2] PowerPulse.Net:

www.powerpulse.net/powerpulse/archive/

aa_040201b3.stm

[3] Cadex: www.cadex.com

[4] Batteries in a portable world:

www.buchmann.ca/default.asp

[5] Li-ion characteristics:

www.buchmann.ca/Article9-page3.asp

[6] LG:

http://battery.rnd.lgchem.co.kr/english/ﬁle/

LG_Li-ion.pdf

[7] NASDA:

www.nasda.go.jp/lib/nasda-news/2002/

09/front_line_e.html

ible shape, is applied in, among oth-

ers, PDAs.

All of these battery types have

their own advantages and disadvan-

tages. A good overview of their char-

acteristics may be found at the

Digit-life.com website [1].

If we are to believe the results of

tests carried out by consumer organ-

isations in different countries, mod-

ern NiCd and NiMH batteries differ

only marginally in performance. The

infamous memory effect associated

with NiCd batteries has practically

disappeared. And yet, some tests

found on the Internet still claim the

opposite and as always it is hard to

tell who is right in such cases. The

characteristics may be specific to

certain brands or types, but in gen-

eral these battery types can now be

said to have similar characteristics.

Li-Ion is often considered the

ideal battery for mobile and portable

equipment: lots of capacity at small

size, little self discharging and a low

internal resistance. On the down

side, Li-Ion is critical in respect of

charging. Thanks to all kinds of

smart chemical links in these batter-

ies, the otherwise very explosive

Lithium is constrained. Unfortu-

nately, the excellent reputation of Li-

ion has suffered somewhat by a

number of articles in German com-

puter magazines, their research indi-

cating that Li-Ion batteries are

affected by natural ageing caused by

the intrinsic chemical composition.

Apparently, it is irrelevant if the bat-

tery is actually used or not. Accord-

ing to these reports, a Li-Ion battery

has only half the nominal capacity

after a year or two. According to the

testers, the industry assumes that

laptop PCs and GSMs have an eco-

nomic life cycle of just two years in

any case. This is also said to apply to

new batteries for GSM phones or

laptops. After all, a battery that has

been left in storage for a number of

years may already have lost a part of

its capacity although the full price is

charged for it! Most manufacturers

remain silent about this alleged

characteristic of their Li-Ion batter-

ies and usually do not print a pro-

duction date on their product.

On the Internet, several websites

may be found covering the above

mentioned effect, for example, the

article Choosing a Battery that Will

Last on PowerPulse.net [2]. Most

other information we came across on

the Internet is based on research

and articles by Isidor Buchmann of

the Canadian ﬁrm Cadex [3]. Cadex

is a manufacturer of, among others,

battery analysers. Buchmann also

runs his own website called Batter-

ies in a portable world [4], which

contains some interesting articles on

battery-related subjects. For

instance, a description of the char-

acteristics of Li-Ion batteries is ren-

dered in [5]. From his research Buch-

mann concludes that Li-Ion cells also

age if they are not actually used.

After about two years, this process has pro-

gressed to the stage where the batteries

often fail altogether.

Little or no information on this subject may

be found with the manufacturers. After some

searching, we came across a datasheet from

LG [6] about their Li-Ion batteries. A graph is

shown indicating that after 6 months of shelf

storage the capacity of a Li-Ion battery

degrades to about 90% of its initial value, and

not owing to self-discharging! These ﬁgures

apply at an ambient temperature of 20 °C —

at higher temperatures the same decrease

occurs much sooner.

Unfortunately all our searching produced

just one serious test mentioning this phe-

nomenon. The other sites only refer to it and

have not done any testing themselves. Our

impression is that the ageing effect is depen-

dent on the chemical composition of the bat-

tery, and will therefore differ from brand to

brand. Besides, the technology behind Li-Ion

batteries is being improved all the time, so

the latest types may be expected to be much

better than the ones manufactured a few

years ago.

As an aside, it is worth mentioning that

space agencies and manufacturers of electri-

cally powered cars are busy researching the

application of large Li-Ion batteries. Espe-

cially with satellites, life expectancy of the

battery is a major issue! Up there, a battery

is expected to last 10 years or longer without

any degradation in quality. A nice example of

this may be found at the NASDA website [7].

Maybe the Li-Ion battery is not as bad as

some would have us believe?

(035005-1)

1/2003

Elektor Electronics

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