Battery Power - Fall 2016 - 9
Feature
Rupture Disks for Venting Cells, Packs
Although battery cells and packs typically feature active and passive safety devices and protection circuitry to
prevent or mitigate potential cell failures, the last resort is
typically a mechanical safety vent that is intended to release
the internal pressure of the cell or pack when a specified
pressure is reached.
One of the most popular pressure relief devices for
lower-pressure applications such as lithium batteries is the
rupture disk. Also known as a pressure safety disk or burst
diaphragm, the rupture disk is a passive pressure relief
device long adopted by the oil, gas and chemical process
industries to protect pressure vessels, tanks and other
equipment from overpressurization.
Rupture disks are available in various designs, sizes,
shapes and set pressures and can be installed on cylindrical,
button, prismatic, or pouch cell designs.
However, as battery cells become increasingly smaller,
so must the rupture disks that protect them. This is driving
the need for miniaturized rupture disks as small as 1/8-inch
and challenging an industry in which products for many
decades have been measured in inches.
"As pressure relief devices become increasingly miniaturized, the rupture disk industry is running squarely
into design and raw material challenges that often require
reengineering the product itself," said Geof Brazier, managing director, BS&B Safety Systems, Custom Engineered
Products Division, a major supplier of rupture disks that
has been involved in the lithium battery industry for more
than 30 years.
According to Brazier, this is due to a delicate balancing act between the shrinking diameters of the burst area,
the limitations of the specific raw materials utilized for the
membrane, and the variations in designs required at low,
medium and high pressures.
Fortunately, the rupture disk manufacturer is embracing
this challenge with novel structures and design elements
that have led to a new category of miniaturized options
from 1/8 inch to 1 inch at all ranges of pressure, with larger
nominal sizes suited to battery pack applications that require a greater vent area.
"In many ways it can be like trying to fit a camel through
the eye of a needle."
To resolve this issue, BS&B has created novel structures
that control the reversal of the rupture disk to always collapse in a predictable manner.
This includes, for example, a hybrid shape that combines reverse buckling and forward bulging characteristics
that are pre-collapsed. In this type of design, a line of
weakness is typically placed into the rupture disk structure
to define a specific opening flow area when the reverse
type disk activates.
Small, nominal size rupture disks are sensitive to the
detailed characteristics of the orifice through which they
burst, which requires close cooperation between the rupture disk manufacturer and the user to achieve the optimum mounting and installation arrangement.
"With small size pressure relief devices, the influence
of every feature of both the rupture disk and its holder is
amplified," said Brazier.
For miniaturized products, BS&B manufactures the
rupture disk from Stainless Steel, Aluminum and Nickel
alloys to achieve compatibility with lithium battery operating conditions.
For more information, visit BS&B Safety Systems at
www.bsbsystems.com.
The Miniaturization Challenge
Miniaturization of rupture disks presents unique challenges, best met utilizing reverse buckling technology, said
Brazier. Unlike traditional forward-acting disks where the
load is applied to the concave side of a dome, in a reverse
buckling design, the dome is inverted toward the source of
the load. Reverse buckling disks are typically sturdier than
forward-acting disks, which are thin and difficult to handle,
and as a result have greater longevity, accuracy and reliability over time.
"As burst diameters decrease dramatically it becomes
challenging to design a reverse buckling disk that will reliably collapse through such small orifice sizes," said Brazier.
www.BatteryPowerOnline.com
Fall 2016 * Battery Power
9
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Table of Contents for the Digital Edition of Battery Power - Fall 2016
Improving Lithium-Ion Battery for Future Energy Storage Needs
Protecting Lithium Batteries and Battery Packs from Runaway Thermal Events
Sorting Busbar Choices for Electric Vehicle Power Distribution
2016 Battery Power Resource Guide
Battery Power - Fall 2016 - Cover1
Battery Power - Fall 2016 - Cover2
Battery Power - Fall 2016 - 3
Battery Power - Fall 2016 - Improving Lithium-Ion Battery for Future Energy Storage Needs
Battery Power - Fall 2016 - 5
Battery Power - Fall 2016 - 6
Battery Power - Fall 2016 - 7
Battery Power - Fall 2016 - Protecting Lithium Batteries and Battery Packs from Runaway Thermal Events
Battery Power - Fall 2016 - 9
Battery Power - Fall 2016 - Sorting Busbar Choices for Electric Vehicle Power Distribution
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Battery Power - Fall 2016 - 2016 Battery Power Resource Guide
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