In light of the recent incidents involving two scooters from prominent EV brands bursting into flames, the subject of EV safety has come under the spotlight. Are all lithium-ion battery systems inherently a fire hazard? Are there specific conditions which make it more likely for EVs to catch fire?
Lithium-ion batteries came to be the preferred energy storage solution for consumer electronics and EVs because of their power density. Compared to a lead-acid battery which stores roughly 25 watts-hour per kg or a nickel hydride battery which can store 100 watts-hour per kg, a lithium-ion battery can store 150 watts-hour per kg. Given that lithium-ion batteries are an inescapable part of everyday life, powering everything from our phones to other electronic items, it’s clear that they’re here to stay, until more sophisticated forms of battery technology arrive. The fact that the li-ion battery market is projected to be worth $193.13 billion is testament to the efficacy of the technology and its ability to withstand a multitude of charging cycles and retain energy. While li-ion batteries have proven to be safe by and large, there have been enough incidents with both consumer electronics and EVs to throw their overall safety levels into doubt.
HOW IT WORKS
A lithium-ion battery comprises multiple cells, which contain lithium. Each battery has electrodes at either end, with one containing an anode while the other contains a cathode. The anode and the cathode both contain lithium but are made of different elements with the former being made of carbon while the latter is made of lithium cobalt oxide.
When you plug a lithium-ion battery, a charging current is given to the cell with the lithium ions moving from cathode to anode through the electrolyte that lies in the middle. When it's supplying energy in the form of electricity, the opposite happens where the lithium ions flow from the anode to the cathode. When all the lithium ions have moved to the cathode, the cell is out of charge.
A BATTERY MANAGEMENT SYSTEM
Unlike other battery systems, lithium-ion cells get extensive battery safety functions. The key to managing the battery’s temperature is a battery management system. It’s responsible for both, maintaining cell temperature and managing currents and voltage. All lithium-ion cells also feature a separator which can melt when core temperatures become too high and cease the transport of ions. Another key requirement for a battery system is the presence of proper ventilation. A pressure-sensitive vent can prevent other cells in the battery from catching fire.
A good battery management system is key to a battery pack’s overall health. It protects the battery cell from being overcharged or over-discharged, manages the overall heat levels, checks for loose connection and shorts and constantly communicates with the vehicle’s onboard computer.
WHEN DO THEY POSE A FIRE RISK?
Improper manufacturing, external damage or inefficient or malfunctioning software can cause a lithium-ion battery to catch fire. According to technology platform Ion Energy, excessive heat generation can occur within a failed or damaged cell, leading to what is known as a ‘Thermal Runaway” in which the heat generated from a failed cell can pass on to the next cell, causing a chain reaction resulting in a fire. This can happen when a flaw in manufacturing allows impurities to seep into a lithium-ion cell. Battery management systems can also be compromised when manufacturers try to make a very compact design which can damage the separator.
Lithium is an inherently reactive and flammable substance. At present, li-ion batteries use organic liquid electrolytes to supply charge. While this continues to be the only form of technology available for mass-produced li-ion batteries, manufacturers like Toyota and VW are in advanced stages of testing solid-state batteries, which not only carry a greater charge, but feature solid electrolytes which possess greater immunity against extreme temperatures.
More solutions do appear to be emerging, in the interim while the standardisation of solid-state tech is awaited. According to Techbrief, a California-based tech company, Nanotech Energy Inc has opted for graphene-made electrodes that can prevent thermal runaway. Graphene being an incredible conductor of electricity and a generally strong material, is an excellent way to prevent overheating.
From a consumer point of view, lithium-ion batteries have, statistically, proven to be a reliable form of technology. However, until more flame-resistant forms of technology enter the battery manufacturing process, it’s best to avoid overcharging the battery or keeping it directly under the sunlight. If a battery is portable, do not charge it where you sleep.With swappable battery units, always inspect for external battery damage, as it can be a cause for chemical leaks which can lead to thermal runaways. When running low on charge, ensure that the battery charge doesn’t go below 10 percent before being recharged. Frequent fast charging can also lead to the battery losing its ability to retain charge, with the average EV battery only managing 100-150 fast charging cycles in its life span.