At the heart of an electric vehicle (EV) is its battery which determines the range and power available for your driving experience.
Unlike the batteries in internal combustion engines (ICE) which primarily serve to start the engine and run auxiliaries like the air conditioning or audio system, the battery in an electric car runs everything.
An EV battery pack contains a series of individual cells and takes up majority of the floor estate in the car. With the significant size of it in the floorboard of the chassis, how safe is the battery of an EV?
The main concern is the combustion risk of a battery, and this has to do with the organic liquid electrolyte. It is made of compounds that are volatile, corrosive and flammable. The potential hazards are therefore firstly corrosion, secondly fire, and last of all, the battery potentially exploding.
Factors that compromise the EV battery
Lithium-ion batters are most often used in EVs due to their capacity to store a lot of energy and extract that energy very quickly. But they are susceptible to thermal runaway and cell rupture. In extreme cases this can lead to combustion.
When the battery and its casing get damaged, it could lead to the electrolytes leaking out of the battery or a short circuit.
However, to provide some perspective, just as ICE vehicles have a fuel tank full of flammable liquid, an EV is just as dangerous as an ICE vehicle in any situation where the car has been compromised.
A short circuit causes the battery to heat up faster as it discharges. And the faster it discharges, the more it heats up. Eventually the electrolyte can vaporise and leak out, and it is a flammable gas. Since the battery is strapped to other parts of the car that can act as an incendiary device, a knock-on effect can occur, and events can escalate quickly.
Over-charging can also cause a short-circuit. When too much energy is pushed into the cell, it can create a build-up of pressure and that will weaken the structure of the cell. Potentially causing a runaway chain reaction.
To reduce these risks, lithium-ion battery packs contain fail-safe circuitry that shuts down the battery when its voltage is outside the safe range.
How we charge our EVs is a crucial part of Battery Safety. Charger manufacturers have to adhere to strict regulations and safety standards, ensuring the quality of the charger. But some dangers remain:
Irresponsible use of a ‘granny cable’ (in cable control box, ICCB, cable)
Hiring an under-qualified person to install your charger
Use of inappropriate and low-quality materials for cabling and electrical works
Cutting corners to save a few dollars here is probably not wise considering the compromise is your health and safety.
Ensuring battery integrity
Battery Management System
Each EV is equipped with a battery management system (BMS). The role of the BMS ensures the safety of the battery by keeping them cool. This software also allows the car to control how our vehicles are charged, discharged, and to monitor the health and safety of the battery pack.
Every EV has a buffer such that you do not have full access to the full capacity of the battery power. An electric car’s battery capacity is expressed in terms of kilowatt-hours, which is abbreviated as kWh. A battery with a 50kWh capacity may only give you access to 45kWh access to do the driving. And when the dashboard says 100%, it is not really a 100% state of charge, it is the cell voltage of the individual cell level.
EV Batteries are mounted on electric vehicles after passing stringent capability tests for verification. These entail and are not limited to:
- Vibration test
- Thermal shock
- Mechanical shock
- Watertight and immersion
- Fire resistance
For more information, check out the UN ECE R100.
In the vast majority of cases, batteries work for their lifetimes without issue. There are millions of li-ion batteries in application all around us in our phones, our laptops, our children's toys, etc.
The car industry is also improving the safety of EV batteries by researching the possibility of using solid-state electrolytes instead of liquid ones, which can minimise overheating issues and fire risks.
Technology has improved and will continue to improve to make these products both more efficient and safer.