Over the last five days, there have been at least four reported incidents of two-wheeler electric vehicles (made by the likes of Ola, Okinawa, and Pure EV) abruptly bursting into flames, bringing to the fore safety issues related to such vehicles, especially the batteries that power them.
EVs are powered by lithium-ion batteries, of the kind used in cellphones and smartwatches, which are generally considered to be efficient and light compared to their counterparts. However, they may also pose a fire risk, as evidenced by the recent incidents.
From electric cars to smartphones to laptops, lithium-ion (Li-ion) batteries are the most popular battery type today, powering millions of consumer electronics around the world. A Li-ion battery consists of an anode, a cathode, a separator, electrolyte, and two current collectors. The anode and cathode are where the lithium is stored, while the electrolyte carries positively charged lithium ions from the anode to the cathode and vice versa through the separator. The movement of the lithium ions creates free electrons in the anode, which creates a charge at the positive current collector.
The key things that make a Li-ion battery better than other kinds and more suited for things like electric cars and smartphones are its light weight, high energy density, and ability to recharge. Apart from this, Li-ion batteries also typically have a longer lifespan compared to lead-acid batteries.
A Li-ion battery can typically store 150 watts-hour per kg as compared to a lead-acid battery, which stores only around 25 watts-hour per kg. In simple terms, it means that Li-ion batteries offer more efficiency compared to other battery types while keeping the form factor of a product relatively compact, which means an electric car fitted with Li-ion batteries will have a greater driving range, and smartphones will last longer through the day.
However, one of the biggest benefits of Li-ion batteries—their high energy density—can also be a potential reason behind the battery’s undoing. According to a blog post by two-wheel EV maker Ather Energy, Li-ion batteries’ high energy density means these cells can become unstable in certain conditions, hampering functionality. They work best within a safe operating limit. A battery management system (BMS) is applied to a Li-ion battery to make sure it operates safely.
A BMS is basically an electronic system that is connected to all the cells in a Li-ion battery pack and constantly measures their voltage and the current flowing through them. A BMS is also equipped with a myriad of temperature sensors, providing it with information on temperatures at different sections of the battery pack. All this data helps the BMS calculate other parameters of a battery pack, like the charging and discharging rate, battery life cycle, and efficiency.
The actual reasons behind the Ola and Okinawa EVs catching fire are currently unknown, as the companies have said they are investigating the matter. However, Okinawa said that from its preliminary observations, based on "credible sources, the media and local authorities," the fire in its scooter was a result of a short circuit due to "negligence in charging the vehicle."
However, these examples also serve as a cautious reminder of the consequences of faults within a Li-ion battery pack. According to industry experts, a number of reasons, such as manufacturing defects, external damage, or faults in the deployment of the BMS, could result in these batteries becoming a fire risk.
On the other hand, temperature, experts pointed out, plays a tricky role in a Li-ion battery pack. "While Li-ion batteries typically perform better in warmer temperatures, extremely high temperatures could mean the battery pack’s ambient temperature could shoot up as high as 90-100 degrees, which is when they become extremely prone to catching fire," a representative of an EV manufacturer said, requesting anonymity.
Aside from that, EVs and electronic devices are equipped with hundreds of batteries together in a battery pack. This means that even if a few batteries malfunction and cause a short circuit, it can kickstart a chain reaction resulting in a fire, given that a battery pack is tightly packed with a number of Li-ion cells. This effect is called thermal runway, which, according to experts, is the reason why Li-ion batteries burst into flames immediately.
Apart from this, prior accidents of a vehicle that may have damaged the battery pack could also sometimes lead to it catching fire after a few cycles of charging.
Reacting to the recent incidents, in a media interview, Tarun Mehta, founder of Ather Energy, said manufacturers are not taking enough time to design products and that testing standards laid down by government bodies may not be enough to test all real-life situations accurately.
As the companies themselves carry out internal investigations into the incidents, the Ministry of Road Transport and Highways has ordered a probe into the vehicles' catching fire abruptly, and is learnt to have reached out to the Centre for Fire, Explosive and Environmental Safety (CFEES) to carry out investigations.
There have been a number of instances where devices or vehicles powered by Li-ion batteries have erupted into flames. Two of the instances that particularly stand out are Samsung’s Note 7, and a Tesla Model S that caught fire while it was standing in a parking garage in Shanghai.
In the case of the Tesla incident, the company said the fire was caused by a single battery module located at the front of the vehicle and that its investigation found no other system defect.
In Samsung’s case, which impacts thousands of its smartphones in the Note 7 series, the company largely found manufacturing defects to be the reason behind the fire — in some cases, the insulation tape around the batteries was missing, resulting in short circuiting, and some batteries had sharp protrusions inside the cell that led to damage to the separator between the anode and cathode.