Fire Safety Breakthrough in Defense Vehicle Li-Ion Batteries
By Felix Frisch, VP Sales and Marketing, Epsilor Electric Fuel
The military vehicle industry was one of the first ones to adopt lithium ion battery technology during the last decade.
With quadruple energy density, high power rates and superior life cycles, Li-ion batteries are favored by most military vehicle developers and advanced armored corps.
At the same time, safety hazards arising from the use of lithium batteries, and their anticipated behavior in case of thermal runaway, are causing many military organizations to cautiously wait for a significant improvement in this field prior to allowing wide integration of this promising technology into their main vehicle fleets.
Despite their technical and operational advantage, the major obstruction to the wide adoption of lithium batteries is the risk of fire and explosion. Widely used in military applications for almost two decades and in the emerging electric vehicle sector, lithium batteries are still considered by armies as safety hazard. The caution is due to the high-profile reports of battery thermal runaway in cell phones, tablet computers and sometimes also in cars. Moreover, in military applications, batteries are subject to combat related risk such as bullet penetration where the vehicle must ensure a safe recovery of its crew from the threat zone.
A possible breakthrough in lithium battery fire safety has been recently announced by Epsilor Electric Fuel, an Israeli based defense battery manufacturer after the completion of bullet penetration tests last January.
The tests demonstrated how two different types of lithium batteries – Li-Ion NCA battery and Lithium-Ion LFP battery – can contain thermal runaway in the severe case of bullet penetration without causing a heavy risk to vehicle crew. Moreover, the company has demonstrated how a battery compartment of a defense vehicle, full of lithium batteries, can continue operating after one of the batteries inside it caught fire as a result of a direct hit.
In new vehicles this can be tackled by enclosing the batteries in compartments that reside outside the vehicles. In older vehicles the challenge is greater, as the batteries are housed inside the vehicles.
Formulating a solution is even more complicated taking into consideration that different armies present different requirements regarding the usage of Li-ion batteries. The US army Ground Vehicle Systems Center (GVSC) main requirements in accordance to the new MIL-PRF-32565B regulation are that thermal runaway must be restrained both when the battery is penetrated by a projectile (bullet or nail) or is exposed to temperatures in excess of 500 degrees C. The latter requirement is considered by most to be extreme and appears to be particularly relevant to naval situations where the crew cannot evacuate from a vessel.
The Israel Defense Force (IDF) armored vehicles are equipped with battery compartments external to the crew compartment. Their main requirement is that in case a battery compartment experiences a direct hit by enemy fire, the vehicle should be able to continue its mission or to evacuate the crew to safety. This can be achieved by using batteries with lower energy rates, or by placing batteries in fireproof materials that will prevent fire propagation between a burning battery and a neighbouring battery that needs to stay operational.
In a series of tests that took place in December 2019 and January 2020, Epsilor exposed two of its products to 7.62 mm armor piercing incendiary bullets shut from an AK-47 assault rifle. Although thermal runaway caused both batteries to burn, in both cases batteries did not explode and presented positive results.
Lithium-ion LFP 6T batteries (Type ELP-02426) are designed to be installed within crew compartments. Epsilor’s 6T LFP battery is covered by an integral steel case incorporating a directional pressure relief. When installed on armored vehicles, such pressure relief is directed towards external parts of the vehicle or towards a manifold, enabling safe release of pressure and gas to the open air outside the vehicle.
After being penetrated by a bullet the battery ignited moderately, releasing steam. The battery burned for some 20 minutes, however, no solid particles were released from the battery and it did not explode or disintegrate.
Lithium-ion NCA batteries (Type ELI-52526) have superior energy capacity of approximately two LFP batteries or four Lead-Acid batteries of the same size. These batteries are designed for installation outside crew compartments. This battery was installed in a fireproof composite case aiming to prevent battery disintegration as well as fire propagation to neighboring batteries. This battery burned for approximately 45 minutes, next to another similar battery, contained in a separate fireproof case. During the test the neighboring battery did not catch fire, and it continued to operate and to generate power after the end of the test.
The outstanding results demonstrate that 6T lithium batteries can be designed to address the most painful aspects of implementing lithium batteries in armored vehicles and can be safely used onboard military vehicles in battle and ensure mission continuity.
This article was published on March 24, 2020 in the ISRAEL DEFENSE website.