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IEC-EN60950-1

Use of Low Resistivity Surface Mount PPTC in Li-ion Polymer Battery Packs

Littelfuse, Inc 

Application Note:

Use of Low Resistivity Surface Mount PPTC

in Li-ion Polymer Battery Packs

Li-ion and Li-ion polymer chemistry has speci c energy

of 400Wh/L at 20°C, which is approximately two times

the speci c energy of NiMH (nickel metal hydride) and

four times that of the old NiCd (nickel cadmium)

chemistry. Li-ion chemistry also operates at higher

voltages of 3.0–4.2V versus 1.0–1.2V for the older

chemistries. The older chemistries had a moderate-to-

high tolerance to over-charging events, whereas the

newer Li-ion chemistry has a very low tolerance to

over-charging

There are a variety of reasons for battery pack failures:

poorly designed cells, lack of over-current/over-voltage

protection, lack of thermal protection, no tolerance to

swelling, no venting methods for gas, and use in high

temperature environments.

Over-discharge and over-charge are two externally

created events that can cause problems in LIBs. During

over-discharge, if the cell voltage drops lower than

approximately 1.5V, gas will be produced at the anode.

When voltage drops to less than 1V, copper from the

current collector dissolves, causing internal shorting of

the cell. Therefore, under-voltage protection is required

and is provided by the battery protection IC. Over-charge

creates gassing and heat buildup at the cathode when

cell voltage reaches approximately 4.6V. Although

cylindrical cells have internal protection from pressure,

activated CIDs (current interrupt devices) and internal

PTCs (positive temperature coef cient discs that

increase in resistance when heated), Li-polymer cells

do not have internal CIDs and PTCs. External over-

voltage, over-gas, and over-temperature protection is

especially critical for Li-polymer cells

Li-ion Battery Safety Standards

Several safety agency standards apply to lithium-ion

battery packs. These are the key standards that govern

the performance, safety testing, and transportation of

lithium-ion battery packs:

● UL 1642-2005, Standard for Lithium

Batteries—Requirements are intended to reduce the

risk of re or explosion when lithium batteries are

used in a product.

● IEC 62133:2002, Secondary cells and batteries

containing alkaline or other non-acid electrolytes—Safety

requirements for portable sealed secondary cells, and

for batteries made from them, for use in portable

applications.

● IEC 62281, Safety of primary and secondary lithium

cells and batteries during transport—These

requirements cover portable primary

(non-rechargeable) and secondary (rechargeable)

batteries for use as power sources in products.

● UL 2054, Standard for Household and Commercial

Batteries—These requirements are intended to reduce

the risk of re or explosion when batteries are used in

a product.

● UN/DOT (Dept of Transportation) Manual of Tests and

Criteria 4th Revised Edition Lithium Battery Testing

Requirements – Sec 38.3.

● IEEE 1625 - IEEE Standard for Rechargeable Batteries

for Multi-Cell Mobile Computing Devices

● IEEE 1725 - IEEE Standard for Rechargeable Batteries

for Cellular Telephones

● IEC/UL 60950-1, Information Technology Equipment

Safety—Limited Power Source, Sec 2.5, Table 2B,

requirements to limit current to less than 8A within

5sec ; this speci cation would apply to most battery

systems used for notebook computers, cell phones,

and tablet devices.

These standards guide manufacturers/suppliers in

planning and implementing the controls for the design

and manufacture of lithium-ion (Li-ion) and lithium-ion

polymer (Li-ion polymer) rechargeable battery packs.

The typical safety-related tests in these standards,

which involve the use of external and internal battery

pack protection, will include the following (standards will

each have their own speci c requirements and this is

just a brief summary of the types of tests conducted):

©2012 Littelfuse, Inc

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