Comparative safety study of Lithium ion Batteries
March 2013
The safety of lithium ion batteries has
been called into question recently by
several high profile incidents.
There are numerous lithium ion technologies and
each has its own safety factor profile.
This report aims to differentiate the safety
factors between two commonly used lithium ion
technologies, namely:
(1) Lithium Metal Oxides such as Lithium Cobalt
Oxide (LCO)
(2) Lithium Metal Phosphates (LMP) such as
Valence’s Lithium Iron Magnesium Phosphate
Lithium ion batteries, by definition, are energy storage systems. As such, if subjected to abusive
conditions, the energy in the systems can be unexpectedly released, thereby presenting safety
issues. Since different lithium ion technologies exhibit different safety profiles, the challenge of
mitigating safety risks in any application rests with choosing the right lithium ion technology for the
application.
Cont’d
The technology of choice for small format applications has been lithium cobalt oxide. For example, the
battery type most commonly used in cell phones and laptops uses lithium cobalt oxide (LCO). LCO has
a greater energy density than the lithium metal phosphates LMP. The greater energy density in LCO
in such small, portable devices has led to its adoption as an acceptable solution in such small format
applications. However, there have been numerous reports of battery related safety issues even in such
devices as laptops and cell phones. Over 45 million cell phone batteries and over 10 million laptop
batteries using LCO technology have been recalled due to safety concerns of the batteries catching fire
or exploding.
In such small, portable devices the risk of adverse events can generally be managed. It is well accepted
in the battery industry that certain safety concerns such as the risk of fire or explosion during the use of
batteries can be addressed by using electronics or other external (to the cell) safety devices to reduce
the safety risks inherent in a battery application. However, such electronics and external devices do
not address safety issues that arise from the choice of chemistry of the cathode material.
Various new markets are seeking to migrate lithium ion technology into their applications due to the
benefits offered by lithium ion over older battery technologies, such as lead acid, nickel cadmium and
nickel metal hydrides. Many of these new markets are in a large format application due to the markets’
requirement for more energy.
In such large format applications, the choice of cathode material becomes more critical with respect to
its inherent chemical safety factors.
The use of lithium metal oxides such as LCO in large
format applications has demonstrated the safety
risks associated with its choice for large format
applications. The recent reports of adverse events
in the use of lithium metal oxide technology such
as LCO in cars, buses and now airplanes, have
raised serious concerns regarding the use of that
lithium ion technology in large format applications.
In such large, fixed format applications the risk
of adverse events is not as readily managed nor
can it be tolerated as in the small, portable device
applications.
Cont’d
There are a number of abusive tests that illustrate the difference in safety
between lithium ion technologies.
Comparative study Table 1
Test Results
LCO
Nail Penetration Test
Pierce cell with metal nail to cause internal short
x
Round Bar Crush Test
Slow crush to deform cell and cause internal short
Abnormal Charge Test
3 x recommended charge rate for 48 hours
- no restrictions
Extended Hot Box Test
150°C exposure for greater than 10 minutes
Bullet Test
Multi-cell Pack Abuse Testing
Series/Parallel Test
Multi-cell Pack Abuse Testing
Pass
Fire
x
Pass
Fire
x
Pass
Fire
x
Pass
Fire
x
Pass
Fire
x
Pass
Fire
Cont’d
Comparative study Table 2
Nail Penetration test Example
LCO Cell
Extreme reaction,
explosion, sparks
and fire.
Valence Cell
No adverse reaction
when pierced.
Not all batteries are created equal
Valence has been serving multiple markets for over 6 years and currently offers a standard range of
products known as the U-Charge battery system. The system comes complete with a fully integrated
Battery Management System (BMS) for large format applications.
Our proprietary Lithium Iron Magnesium Phosphate based batteries offer high energy and power
densities without compromising safety along with robust high and low temperature performance and
best in class Cycle Life.
Cont’d
Comparative study Table 3
Performance Characteristics
LCO
x
Prone to Thermal Runaway
No
Yes
High
Very High
Very Good
Poor
Very Good
Poor
Very Good
Poor
Initial Capacity
Capacity Fade
Life Cycle
Temperature Performance
x
x
x
Note: No matter how many safety features are installed, design rules followed and standards are
met the risks can never be eliminated completely, however the choice of an inherently safe chemistry
further reduces such risks.
For more information about the safety of Valence’s LiFeMgPO4 Batteries please see:
Safety Video: http://www.valence.com/why-valence/safety
3rd Party Exponent Safety Report: http://www.valence.com/sites/default/files/exponent_report.pdf
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Performance may vary depending on, but not limited to cell usage and application.
If cell is used outside specifications, performance will diminish. All specifications
are subject to change without notice. All information provided herein is believed,
but not guaranteed, to be current and accurate. Copyright © 2005-2013 Valence
Technology, Inc.
www.valence.com
Mar 2013
Valence Comparative
Safety Study Report