As EVs catch fire, lithium ion batteries remain at the heart of the problem

If not managed properly, the lithium ion cells used in electric vehicles can become overheated and cause fires

Over the past week or so, images of electric two-wheelers going up in flames have sparked concern over the safety of these vehicles. And days after an Ola Electric scooter caught fire and caused a social media uproar about the growth-at-all-costs nature of unicorn companies, two-wheelers of two more electric vehicle (EV) startups — Okinawa and Pure — suffered the same fate.

Why are such incidents happening? Industry experts believe this is a technology challenge that automakers face globally, rather than just in India, and that the lithium ion cells used in EVs are at the heart of the problem. 

“Fundamentally, why EVs catch fire is that lithium ion cells can go into something called a thermal runaway,” says Arun Vinayak, co-founder of EV startup Exponent Energy. “It means the heat generated within a battery exceeds the heat dissipated to its surroundings — and generally happens when the cells heat up beyond a few hundred degrees Celsius.”

Hence, it is important to not only design batteries with utmost care to prevent incidents like short circuits, they also need to be managed arefully within the EV through software and sensors.

“One of the most important factors is mismanagement of cells. The primary job of a battery management system (BMS) is to control how fast they are charged, and what load and temperature they operate in. The BMS ensures that the powertrain of the EV is operating in a safe zone,” says Varun Agni, chief technology officer and co-founder of Bounce.

For example, Bounce’s electric two-wheeler has a motor with a peak load of 2 kilowatt, while its battery can store energy of around 2 kilowatt hours. This means that there is never more than one coulomb (a unit of electric charge) of discharge. Exceeding this could cause battery deterioration. 

Overheating problem

“Usually, the thumb rule is that the battery capacity and the motor capacity should be similar. In layman’s terms, the power drawn is continuous if the motor’s capacity is much higher than the battery capacity. And this might lead to problems like overheating,” says Vivekananda Hallekere, co-founder and CEO of Bounce.

Experts note that though it is critical for EVs to have a healthy battery, some EV companies overlook this by using cheaper, poor-quality cells with shorter lifespans. Another trend of concern is the adoption of fast-charging to make EVs more attractive for customers.

“Fast-charging should be avoided, as putting in too much energy in too short a time is likely to hurt the battery. In our charging, we never go into the unsafe zone and do it at a 0.5 coulomb. Even 1 coulomb or 2 coulomb is all right, but fast-charging generally happens at upwards of 4 coulomb,” explains Hallekere.

The contrary view is that while fast-charging may affect the lifespan of the battery, it is not likely to cause fires. “Things like that happen when there is uncontrolled current and as a result of a short circuit. Even if you draw 200 amperes of current, it won’t cause a thermal runaway,” says Vinayak of Exponent Energy.

No perfect answers

But if there is a short circuit in the cells and the current is travelling through an alternate path without any resistance, there is uncontrolled current, which may lead to a fire. For this reason, EV batteries need to be designed in such a way that there is enough breathing space between cells, so that even if one or two of them are affected by a short circuit, it does not spread to the entire battery.

“There are no perfect answers to what should be the density of packaging, and the like. The only way is to do stress tests on your battery system, push them to the limit while testing and blow them up on purpose. This is because each cell in the market is very different in how it is designed, and hence can have different dynamics and limitations,” says Vinayak.

Experts also reckon that NMC (nickel-manganese-cobalt) chemistries used in lithium ion batteries are prone to causing fires, as they release volatile chemicals. “An NMC battery is definitely more prone to fires and needs liquid cooling, compared to an LFP (lithium iron phosphate) battery, which can work even without liquid cooling. NMC gives a higher performance for a powerful vehicle, but if you need sustained performance you can go to LFP,” says Nakul Kukar, co-founder and CEO of Cell Propulsion, a commercial EV company.

Some reports have it that companies such as China’s BYD Co have been developing EV battery cells that use lithium iron phosphate cathodes, which are less prone to catching fire, but are not able to store as much energy as standard cells that use nickel manganese cobalt cathodes. 

Meanwhile, the Chinese battery maker CATL has unveiled a sodium-ion battery that does not contain lithium, cobalt or nickel. A number of companies, including Toyota, are also developing battery cells with solid-state electrolytes, which could minimise overheating issues and fire risks, but could take another three to five years to commercialise.

“If you compare instances of EVs catching fire today to internal combustion engines when they first started, you will realise that electric is a much safer option already. As the technology gets better with time and EV companies adopt more stringent measures, such incidents will become rarer,” says Kukar of Cell Propulsion. 

BATTERY SAFETY

• Batteries have to be calibrated within the EV through software and sensors called a battery management system
• Some EV companies may be overlooking battery health by using cheaper cells of poorer quality and having shorter lifespans
• There needs to be enough breathing space between cells, so even if one or two of them are affected by a short circuit, it does not spread to the entire battery