Coin Cell Battery Safety?
I've never heard of a "safe" battery for sale.


Lead acid - Gee, Lead and Sulfuric acid... totally not safe.
Alkaline - not too dangerous to you (read: Less dangerous but still caustic), but when they leak, your electronics are gone.
Nickel Cadmium - Cadmium, that's poisonous if it breaks.
Nickel Metal Hydride - Hydrides are extremely reactive.
Lithium anything - Lithium will literally burst into flames on uncontrolled contact with oxygen. So don't puncture one.


There are a few prototypes for safe batteries going on. Al-ion, nickel film protected Li-ions, etc. But, those aren't available.

Instead, You should make sure that the Li chemistry you're using isn't Li-FePO3 (this one is the most dangerous of the Li-ions), and protect the battery from over-heating by creating a circuit that cuts off current from the battery if the battery becomes too hot. Heat is the most dangerous thing that Li-ions go through, since they are generally very well sealed against outside oxygen getting to the lithium. Also using a standardized connector so that the battery can be replaced after a few years will help give the project some longevity and keep it safer. As batteries age they become more prone to failure, catastrophic or otherwise.