Browse Prior Art Database

LITHIUM ION BATTERY WITH IMPROVED SAFETY THROUGH USE OF INTERNAL PTC

IP.com Disclosure Number: IPCOM000008904D
Original Publication Date: 1999-Jan-01
Included in the Prior Art Database: 2002-Jul-23
Document File: 2 page(s) / 110K

Publishing Venue

Motorola

Related People

Mike Fulcher: AUTHOR [+3]

Abstract

Lithium-ion battery technology has several unique safety concerns relative to traditional aque- ous battery chemistries. Under abuse conditions, a lithium ion cell may overheat, leading to ignition of the flammable organic electrolyte in the cell. Examples of common abuse conditions are 1) short- circuit, creating very high currents in the cell; and 2) overcharge, where continuous charging above the cell voltage limit leads to thermal runaway.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 60% of the total text.

Page 1 of 2

MOTOROLA Technical Developments

@

LITHIUM ION BATTERY WITH IMPROVED SAFETY THROUGH USE OF INTERNAL PTC

by Mike Fulcher, Paul Gies and Jason Howard

  Lithium-ion battery technology has several unique safety concerns relative to traditional aque- ous battery chemistries. Under abuse conditions, a lithium ion cell may overheat, leading to ignition of the flammable organic electrolyte in the cell. Examples of common abuse conditions are 1) short- circuit, creating very high currents in the cell; and 2) overcharge, where continuous charging above the cell voltage limit leads to thermal runaway.

  A common safety feature in L&ion technology is the incorporation of a "positive thermal coefficient" (PTC) device, often referred to as a "polyswitch". This device, connected in series with one of the cell tabs, will increase in resistance at elevated tempera- tures thus limiting the current flowing through the cell. These devices provide excellent short circuit protection and can also help "shutdown" during overcharge.

  One issue with PTC's is appropriate attachment to the cell. The device may be attached externally to the cell, however, this is mechanically difficult with the soft, flexible packaging of Li-ion polymer cells and allows for purposeful or accidental removal of the device. Furthermore, thermal con- ductivity from the cell to the PTC will not be effi- cient. An additional problem facing Li-ion polymer technology is short circuits through the metallized packaging mate...