As found with the hoverboards that were catching fire last year and more recently with the combusting S7 smartphone, some battery compositions like lithium cobalt oxide can be unstable if not charged in the correct manner.
However, there are currently 46 different compositions of lithium batteries and not all of them have a history of exploding.
The lithium batteries that you will find in modern emergency lighting applications use iron phosphate as the cathode material. These particular batteries are known as lithium iron phosphate (LiFePO4).
LiFeP04 is becoming the preferred choice for emergency lighting, not only because the batteries are physically smaller, but because they draw far less power when they are charging. LiFe04 can also last double the life of traditional emergency lighting batteries such as nickel cadmium or nickel metal hydride.
The UK's emergency lighting control gear manufacturers have carried out extensive research into LiFePO4 batteries and have found that they are the safer option.
Manufacturers have also added protection circuitry to the batteries, which allows them to shut down in the event of any issues that may lead to a fire, such as a short circuit or over charging.
I personally feel that these batteries are far safer thanks to the aforementioned safeguards. My advice is to ensure that the type of battery being used with any emergency control gear or emergency luminaires is LiFePO4.