Challenges in high-energy-density batteries

[mhagmann]

The present quest for batteries with higher energy densities to provide greater range in electric cars and increased performance in electronic devices should be be made with great care. To date I believe that the highest specific energy (SE) for available lithium-based materials is 2.0 MJ/kg, whereas TNT and ANFO have similar values of 4.6 and 3.7 MJ/kg. Recently SiNode Systems claimed to have increased the SE by a factor of 10 by incorporating graphene in experimental lithium-based materials. I am more concerned about the possibility of a true detonation than the fires that have already been reported. When a material has the energy density detonation will occur when there is the right combination of surface chemistry, contaminants, etc. Our society learned about the danger of wax coating on ammonium nitrate in the Texas City Disaster of 1947, and discovered that nitromethane is an explosive in the tank car explosion at Mt. Pulaski, Illinois in 1958. I would appreciate any comments regarding how this issue is being addressed.

 

[Staf_Verhaegen]

I don't see the correlation between electrical energy density and energy density when buring and exploding. For example even an almost empty Li-ion battery will hurt seriously when catching fire.

 

[mhagmann]

In the advanced batteries now under development there is an exothermic chemical reaction with an energy density comparable to or exceeding that of high explosives. If you did a DTA (differential thermal analysis) on a small sample containing each of the components I would expect to see a strong exotherm with autoignition consistent with the calculated energy density. However, all of the reactants must be contained during the DTA. For example, a mixture of finely powdered aluminum with water will detonate with a booster but the exotherm is not seen on a DTA if the water evaporates first. A sudden input of energy to this small sample would probably cause detonation but I would not expect this with a new battery because the anode, cathode, and electrolyte are not mixed as finely-divided components. However, after repeated charging and discharging of the battery the integrity of the electrodes is likely to be compromised which may cause mixing with fine “whiskers” and finely dispersed powders. Please do not confuse true detonation with “explosions” and fires that have already been reported.

 

[IanD]

This is just FUD -- so petrol is perfectly safe and never burns, catches fire or explodes? Any medium which stores a lot of energy can "explode" if things go wrong, this includes petrol, hydrogen, batteries, flywheels, superconducting storage -- an explosion just means all that energy escaping rapidly when it's not supposed to. I'd be very surprised if such high-energy-density batteries aren't much safer than inflammable fuels, which is what they'd be replacing.

 

[mhagmann]

IanD: Just a quick technical answer--The word "explosion" is often used to refer to a chemical reaction where a fuel combines with oxygen from the air, so the rate of the chemical reaction is limited by the influx of oxygen. However, a detonation occurs with a self contained device that does not require oxygen. For example, the detonation velocity of TNT is 6,900 meters per second, and increases with the energy density of an explosive. The energy stored in a flywheel would also be released in a manner that would not be rate limited by requiring oxygen. Danger is a part of life, but I have mentioned the possibility of detonation in high energy density batteries to complete a "rosy" picture that has been described by others.