Why does Lithium-ion battery catch fire?

With recent incidents of fire in EV Scooters (two-wheelers) in India, people are worried about the safety of electric vehicles. These incidents happed in these brands of two- wheelers – OLA, Okinawa & Pure EV.

As we know that all electric vehicles get power through Lithium-ion batteries. Lithium ion batters are used these days in many electronic devices like laptops, mobile phones, smart watches etc as well as electric vehicles. The main reason of using these batteries is the higher storage capacity of power per Kg as compared to other batteries so that these devices could run for longer duration in single charge. Generally, the present energy storage capacity of Li-ion batteries is 150 watts-hour per Kg as compared to 25 watts-Hour per Kg for Lead Acid battery.

Design of Lithium-Ion Battery–

The design of battery is slightly different, it consists of an anode, a cathode, separator & electrolyte. The Anode, Cathode & Separator are assembled in a metal case/container where they are submerged in an electrolyte. In this configuration Anode (Lithium-cobalt-oxide) acts as a positive electrode while cathode (carbon) acts as a negative electrode. These two electrodes are separated by a thin sheet of separator which is made up of micro-perforated plastic. Generally, ether is used as an electrolyte.

Working of Lithium-ion Battery –

Working of Lithium-ion battery is different from normal lead acid batteries. In Lithium-ion batteries, ions are transferred between anode & cathode during charging & discharging of batteries while chemical reaction is required in conventional batteries.

During charging of batteries – lithium-ions are transferred from anode (positive electrode) to cathode (negative electrode) & during discharging – Li-ion moves back to anode from cathode & thus complete the cycle of battery. Per cell of Li-ion battery produces 3.5V which higher than any other type of batteries.

BMS of Lithium-ion Batteries –

Because of its usage for commercial purpose, Battery Management System (BMS) is used in all Lithium-ion batteries of electric vehicles for the safety of the batteries. The main function of BMS is to manage the temperature of battery. It also manages current & voltage of the battery. A good health of Li-ion battery depends on BMS which must ensure following things –

• Protection of battery cell from overcharged / over-discharged,
• Manage heat levels of the cells,
• Checks loose connection & short circuits if any,
• Communicate with vehicle onboard software

Precautions required to avoid fire risk while using Li-ion batteries –

Following points are important to avoid fire in Lithium-ion batteries –

• Separator plays a very important role in the safety of the battery. As we know that anode & cathode are two different charged electrodes & they should not come in contact with each other. Whenever they will come in contact with each other short circuit will occur which may lead to fire. That is why the designing of separator should be done very carefully. If too much thin separator is designed, then chances of contact of both electrodes will be very high.
• Avoid external damage to the battery
• Temperature management of Li-ion battery is very important. Therefore, we need to ensure that BMS software should remain in healthy condition so that temperature management of the battery is done continuously.
• Thermal Runaway Condition should be avoided because it a condition in which heat is transferred to another cell when one cell fails & creates a chain reaction that results in fire in the battery. Therefore, there should not be any compromised in battery management system during manufacturing.