does overcharging _lithium_ batteries release _hydrogen_?

Short answer is: Not under typical conditions and/or with a correct charger. However:

The electrolytes are flammable, and lithium itself is highly flammable. So, if the battery is overcharged and starts to leak, the released materials can cause fires and release a great deal of energy. Or if the battery is physically damaged such as a cracked casing or similar.

Peter WIeck Melrose Park, PA

"Explosion Hazards from Lithium-Ion Battery Vent Gas"

These gases build within the cell and can ultimately lead to rupture of the cell and release of the gases. The gas mixture generated and released is flammable, consisting of various mixtures of hydrogen, carbon-monoxide, carbon-dioxide and various hydrocarbons including methane and propane. Ignition of these gases result in fire and explosion scenarios that pose a significant risk to surrounding life and property.

The article goes on to detail which gasses are produced, under what conditions, and in what proportions, which changes depending on SOC (state of charge).

danny burstein wrote: =================

** Think that is not the most likely scenario.

If ( whatever) gas leaks out under pressure, the cell is the unlikely to explode. That's why many rechargeable cells have vents built in - NiCd, NiMh and alkalines too. SLAs often have no vents and will explode( spraying acid) if over charged at a high enough rates. Strangely, NiCds will too, if charged under freezing conditions.

The most likely *fire hazard* is damage - when there is a short in the wiring or from one cell body to another. The huge current that flows in the next few minutes will cause massive heating and set any flammable plastic involved alight. Then nearby carpets, and furnishings clothing etc.

Lithium Ion ( LiPo ) cells are worse hazards that older types cos of the much greater energy storage per cell. The advice to have your eBike sited outdoors when charging is very wise.

..... Phil

[lots snipped]

Thanks. That article (which, despite coming through Elseveir, is a freebie) is *exactly* the background info I was looking for.

So they seem to agree with me. In a residential setting with a couple of e-bike batteries, the fire risk is almost entirely from "thermal runaway" and not gas production/escape.

Thanks again.

OSTI (US governmint office of scientific and techy info) apparently contracted with Elseveir to handle their distribution. I forgot to mumble something about the article search:

They have 23,135 articles listed under "lithium ion battery safety" keyword search: or 147 under the exact phrase: The first article found is rather interesting: "Materials for lithium-ion battery safety" This Review aims to summarize the fundamentals of the origins of LIB safety issues and highlight recent key progress in materials design to improve LIB safety.

In my never humble opinion, the more likely eBike scenario is mechanical damage, either from modifying or soldering the battery pack cells, or having the eBike crash into something. Also included are high resistance contacts causing the safety fuse to fail to trip, BMS (battery management system) misprogramming or miswiring, and various attempts to convince the eBike to deliver more power. Locally, I've only seen 3 eBike fires and have been told about 3 others. All were the result of owner tampering, shoddy repair, cell replacement, or combinations of these. A commercial eBike system is probably fairly safe. A do-it-thyself mess of mods and repairs is probably not so safe.

Hint: Store your batteries in a fireproof box, preferably with a working smoke alarm nearby: "Underrated E-Bike Battery Fire Hazards Call for Attention on Safe Storage"

Methinks things will be better when the cobalt cathode are replace with LiFePO4 cells.