Fully Electric Vehicles (EVs), also known as Battery Electric Vehicles (BEVs), gain their power from a large pack of batteries instead of burning petrol or diesel, like your standard Internal Combustion Engined (ICE) car does. These batteries are made from Lithium-ion.
To simplify, an electric car is a bit like a mobile phone. A mobile phone gets power from a single Lithium-ion (Li-ion) battery whereas EVs will use a large pack made up of thousands of individual Li-ion cells instead.
Lithium-ion is common across many electronic devices due to its recharging capabilities. They have a high energy density which means that lots of energy can be held within a small space which is perfect for building a car.
Lithium-ion is also safer than many of the alternatives out there. To ensure the safety of drivers, different safeguards have been implemented to protect batteries during repeated rapid charging sessions.
When the car gets charged, electricity makes chemical changes to the Li-ion batteries that are then reversed as the car gets driven, which produces electricity. This process is known as discharge.
The battery pack in an Electric Vehicle will undergo continuous cycles of charge and discharge throughout its lifespan. Over time this causes wear that decreases the vehicle’s electric range slightly, but don't worry, current predictions think that a battery pack could last from about 10-20 years before needing to be replaced.
Capacity and kWh
The capacity of an EV’s battery is expressed in KiloWatt Hours (kWh). A kWh is a measure of energy. For example, a 1,000 Watt drill would need 1,000 Watts (or 1kW) to make it work. Powering that drill for 1 hour would therefore require 1 kWh of energy.
The car’s battery capacity can usually be seen in its derivative, for example, the Renault ZOE 100kW i GT Line R135 50KWh 5dr Auto has a 50kWh battery that has a range of about 239 miles.
An electric motor is a complex piece of engineering, however, the way the battery and electric motor work together can be understood in relatively simple terms.
The Lithium-ion battery pack is linked to one or more electric motors which, in turn, drive the wheels that make the car move. By pressing the accelerator, an EV will instantly convert the stored DC power in the battery into AC power for the motor which gradually consumes the energy stored in the batteries.
An electric car has no alternator to recharge the battery, like that seen in a petrol or diesel vehicle. Instead, the electric motor adopts this role too, when you take your foot off the accelerator the rotor starts spinning faster; this helps to recharge the battery.
Electric motors are very clever because of their ability to send energy back into the battery that would have otherwise been lost.
When a petrol or diesel car brakes, hydraulic fluid pushes the brake pads against the brake discs on the wheels. This process uses friction to convert the kinetic energy into other forms of ‘wasted’ energy that is lost to the surrounding environment. This slows the car down but isn’t particularly efficient.
Electric cars, on the other hand, are far more economical than combustion vehicles because they are able to take this ‘lost’ energy and use it to recharge the batteries to help prolong the car’s range. It’s not a completely perfect process as some energy will still get wasted, but it certainly helps the vehicle in going further on a single charge.
The electric motor in an EV moves in two directions. When moving forwards, the motor acts as normal, converting electrical energy into mechanical energy. However, when put in the opposite direction the motor works as a generator converting mechanical energy into electrical energy.
When you lift your foot off of the accelerator the car’s momentum is used as the tool to turn the motor into reverse and begin storing the kinetic energy for later use. The car will begin to slow down as this process takes place.
Different EVs have different settings for how much regenerative braking occurs when you lift off of the pedal. These settings can be adjusted on personal preference; switching it to the maximum setting will make the car operate almost solely in a single pedal capacity.
In the popular Nissan Leaf, single-pedal driving is called ‘e-pedal’ that can be turned on and off with the switch of a button. A brake pedal will still be present on all EVs if you’re not slowing down as quickly as desired.