COMPARATIVE SAFETY STUDY OF LITHIUM-ION BATTERIES
In March 2013, Lithium Werks (Valence) undertook a comparative study of different lithium-ion battery chemistries. These were the findings:
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 Lithium Werks’ Lithium Iron Phosphate
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LITHIUM-ION = ENERGY STORAGE
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.
CHEMISTRY CAN BE APPLICATION DEPENDANT
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.
SAFETY RISKS OF LCO
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.
There are a number of abusive tests that illustrate the difference in safety between lithium-ion technologies.
|Nail Penetration Test Pierce cell with metal nail to cause internal short
|Round Bar Crush Test Slow crush with metal nail to cause internal short
|Abnormal Charge Test 3x 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