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points by ggreer 1 day ago | 0 comments

Lithium battery energy density is much lower than petroleum, so the difference between a fully charged 100kWh battery (which weighs over half a ton) and an empty one is less than 3 gallons of diesel. Most of the energy expended in a battery fire is from the electrolyte reacting with the cathode material.

Over/under-charged batteries are a safety hazard because they can generate hydrogen gas which can initiate a fire, but the energy released from the fire will be pretty much the same.

[–] jacquesm 1 day ago

Lithium fires are brutal, they're extremely fast and the toxic gases are just as dangerous as the fire itself:

https://www.reuters.com/world/asia-pacific/about-20-bodies-f...

[–] ggreer 1 day ago

If we're going to count industrial accidents, then oil kills way more people. There are deaths from disasters involving wells, refineries, pipelines, tankers, and gas stations. But because they've been happening for over a century, we accept them as a fact of life. Even correcting for the much smaller install base of EVs and lower number of vehicle miles traveled, fossil fuels are far more deadly.

[–] jacquesm 1 day ago

Oh, absolutely, in the aggregate there is no contest here. I just wanted to illustrate how incredibly fast lithium fires can spread.

I've made a bit of a study of this because I use Lithium Ion batteries in volume. I take a lot of safety precautions because I realize full well how dangerous they are. At the same time I have a 25L canister of diesel and another with gasoline sitting around and I have zero expectation of either of those spontaneously combusting.

[–] klaff 1 day ago

The energy released during a fire is higher than what is accessible by discharging the battery. Here's one paper describing ratios from 1.25 to 5 depending on access to oxygen during the combustion.

https://cea.hal.science/cea-05234204v1/document

[–] ggreer 1 day ago

I'm pretty sure you're reading the paper wrong. Of the 29 tests they did, 5 were in air, and all of those were with fully charged batteries. The 5x ratio is the difference between electrical energy stored in the battery and energy released in atmosphere. They did not measure different states of charge versus energy released in atmosphere. That's why the figures for the nitrogen and atmosphere tests are bar charts instead of line charts.

The relationship between energy stored and energy released was mostly determined by how big the batteries were, not their state of charge. Only 4 of their tests varied state of charge, and those were all in vacuum (with cells #1 & #6), and state of charge was never below 60%.

[–] klaff 1 day ago

I wasn't clear, sorry, and you understood the point from the article. I thought you might have been assuming that a 100 kWh battery would produce 100 kWh of energy when burned, and I was trying to point out that when the battery is burned, you can get a much larger amount of energy. My apologies for wasting your time.