Lithium Batteries for Emergency Lighting: Why Effective Thermal Management is Essential

Rechargeable lithium battery technology first emerged in commercial products in the early 1990s and has since grown in popularity. The development of lithium batteries was driven by the need for higher energy density, with portable electronic devices and electric vehicles being the main application areas. However, lithium batteries are now also a popular solution for powering emergency lighting standby applications.
 
This article will explain the reasons behind why lithium batteries are popular when compared to alternative technologies, and will also outline some of the considerations that must be made when specifying battery technology.
 

Lithium is highly flammable in air and moisture, and great care must be taken when manufacturing and using lithium batteries - especially ensuring that temperature limits are not exceeded and the battery casing is not penetrated or damaged during installation. Both of these situations can create a condition known as thermal runaway, which in turn can lead to lithium fires which are particularly difficult to extinguish.
 
Thermal runaway results from the build up of heat and pressure inside the battery, which can trigger chemical reactions, leading to a spiral of more heat and pressure. Careful management of battery temperature has, therefore, become one of the most important parameters when it comes to handling the development and propagation of lithium-ion batteries within emergency lighting.
 

In a thermal runaway situation, the smaller the temperature rise (T-rise), the better. The best chemistry to minimise T-rise - and ultimately, thermal runaway - is lithium iron phosphate (LiFePO₄). LiFePO₄ is also a better solution for standby applications where batteries are permanently in a charged state and only occasionally discharged to full depth.
 
To ensure safe and reliable operation, it is highly recommended that any lithium systems for emergency lighting are supplied with thermal monitoring. This is done by the inverter continuously monitoring the battery case temperature, so that early detection of any runaway situation is achieved, and the system is then inactivated before a critical risk condition is reached.
 

As well as keeping emergency systems safe, it should also be noted that running batteries and associated electronics cooler also delivers more reliable systems with longer service life and longer warranties possible. This rule applies equally to lithium-based systems and also alternative chemistries such as nickel metal hydride (NiMH). Using drivers and inverters with specialised software that offers efficient charging in addition to the thermal monitoring has been shown to improve operating temperatures by up to 10°C, which can effectively double the achievable lifetimes of both the batteries and the associated electronics.


Read the full article on the A1 Lighting website here