Over the past five years, the automotive industry has undergone a significant transformation, with electric vehicles (EVs) becoming increasingly integral to our daily lives. Even for those who don’t own an EV, automotive journals and media are now predominantly focused on electric cars, reflecting their growing prevalence.
However, there’s a general sense of curiosity and sometimes uncertainty about the technology behind EVs. While many perceive electric cars as simpler compared to traditional combustion engine vehicles, understanding EV technology is not as straightforward as it might seem. Text: Luca W. © Images: Renault, Tesla, Volkswagen ©
Table of Contents
🔋 How does an electric car battery work?
Today’s electric cars’ battery lies on one technology only: Lithium-ion, based on a natural chemical reaction between electrically charged Lithium atoms (ions). In fact, it is one common feature with the internal combustion engine, that is also based on a chemical reaction between two molecules (gasoline and air), which is combustion.
The battery is indeed the heart of an electric car, playing a pivotal role in defining its weight, power, range, charging time, and cost. Therefore, optimizing battery usage is crucial for ensuring its performance and longevity.
Units and characteristics
It’s important to recognize that unlike internal combustion engine (ICE) vehicles, where fuel capacity is measured simply in terms of volume (gallons or litres), battery characteristics involve a more complex set of units. The mains are:
- Voltage (V): usually 400 to 800V
- Electric current (A or Amp): depending on conditions
- Electrical capacity (kWh): energy quantity available and defines the effective range; power that the battery can deliver for an hour
Li-ion battery composition
A Li-ion battery comprises several key components:
- Anode: negative when battery discharges
- Cathode: positive when battery discharges
- Electrolyte: medium that allows the flow of electrical charge between the cathode and anode
- Separator: barrier that keeps the cathode and anode from touching each other
- Lithium oxide: primary material used, it is chosen for its stability and high energy density relative to mass
Functioning of a Li-ion battery
The Li-ion battery operates on an electrochemical reaction between its cells to generate electricity.
Charging process
When the battery is fully charged (100% State Of Charge or SOC), lithium ions are stored in the anode. These ions have lost an electron, carrying a positive charge. They are attracted to the negatively charged anode, similar to how opposite poles of magnets attract each other.
Discharging process
When electricity is demanded (e.g., the driver presses the throttle), lithium ions are oxidized, releasing electrons. These electrons flow through the electrical circuit to power the motor, while the lithium ions (Li+) move towards the cathode through the electrolyte. Upon reaching the cathode, the ions reunite with the electrons that have passed through the motor, storing energy in the process.
Recharging process
During charging, the process reverses. Lithium ions move back to the anode, preparing for the next cycle of discharge and power delivery.
🧲 What is a motor in an electric car?
The motor (the engine) plays the role of converting electrical energy, stored in the battery, into mechanical energy. To simplify, it uses the electricity to create rotational force, which drives the wheels of the vehicle.
Compared to internal combustion engines, which have an efficiency of around 35%, electric motors are more efficient, achieving up to 98% efficiency. This is a key advantage of electric cars. Additionally, electric motors are generally simpler in design and require less maintenance than their internal combustion counterparts, contributing to lower operational costs.
Nowadays, the majority of electric cars employ permanent-magnet motors. These motors are favoured for their compact design and higher efficiency, which directly contributes to increased mile range of the vehicles1. The specific types and characteristics of these motors will be discussed in more detail in a separate post.
💨 How far can an electric car go on a single charge?
The driving range of an electric car, or how far it can travel on a single charge, is primarily determined by its battery capacity (the lower the capacity, the lower the range) and the efficiency of its motor. However, electric cars are particularly sensitive to various forms of motion resistance, such as weight, aerodynamic drag, and tire resistance. Engineers must carefully balance these factors to maximize range while maintaining optimal performance and comfort levels.
Consider this example:
- The Tesla Model 3 Long Range is equipped with a 75 kWh battery and boasts a range of 629 kilometers (WLTP standard)2
- The Skoda Eniaq iV 80, despite having a slightly larger 77 kWh battery, has a shorter range of 544 kilometers (WLTP standard)3
The difference in range between the Tesla and the Skoda can be attributed to qualities in design and build. The Skoda Eniaq, being a heavier and higher SUV, faces bigger motion resistances compared to the Tesla. This increased resistance impacts its efficiency, thereby reducing its range despite having a marginally larger battery. This illustrates the complex interplay of vehicle design, weight, aerodynamics, and battery technology in determining the overall efficiency and range of electric cars.
Range optimization
To optimize the range of electric vehicles, car makers and suppliers have developed various technological solutions. One of the most effective being regenerative braking4. This system captures the kinetic energy typically lost during deceleration or braking and converts it back into electrical energy, which is then stored in the vehicle’s battery. Just like a bicycle light generator.
Regenerative braking works by using the electric motor as a generator when the vehicle slows down. Instead of using the brakes, the motor inverts its function, slowing the vehicle while simultaneously generating electricity from the vehicle’s motion. This energy is then fed back into the battery, effectively extending the vehicle’s range.
🔌 How long does it take to charge an electric car?
The charging time for an electric car can vary significantly based on several key factors:
- State Of Charge (SOC): similar to the battery percentage indicator on a phone. It represents how much charge is already in the battery. The lower the SOC, the more charging is needed
- Battery capacity: total amount of energy the battery can store, measured in kWh. A larger battery capacity generally means longer charging times
- Charging power: determined by the power output of the charger and how much power the car’s battery can accept. If the battery’s maximum charging rate is lower than the charger’s power output, the battery’s rate will be the limiting factor
- Vehicle charger/converter characteristics: the onboard charger/converter converts AC (Alternating Current) or DC (Direct Current) from the grid to DC for the battery. The efficiency and capacity of this converter can affect charging speed
- Type of charging station: AC charging stations, commonly found in homes or public places, are slower. DC fast chargers, available at dedicated charging stations (highways), provide much quicker charging
Using the example of a Tesla Model 3 with a 75 kWh battery at a State Of Charge (SOC) of 20%, we can calculate the charging time using a 7 kW AC charger. Here’s how the math works:
- 80% of the battery’s capacity needs to be charged
- 80% of 75 kWh = 0.80 × 75 kWh = 60 kWh
- With a 7 kW charger, the time to charge 60 kWh can be calculated by dividing the required energy by the power of the charger:
- Time = Energy / Power
- Time = 60 kWh / 7 kW = 8.57 hours
Therefore, it would take approximately 8 hours and 34 minutes to fully charge the Tesla Model 3 from a 20% SOC using this charger.
Moreover, using a DC (Direct Current) fast charging station can significantly reduce the charging time. While AC chargers provide power up to about 7-22 kW, DC fast chargers can deliver much higher power levels, sometimes up to 300 kW or more, depending on the capabilities of the vehicle’s onboard charger.
However, it’s important to note that not all EVs can accept the maximum power offered by high-output DC chargers. The actual charging speed will depend on the vehicle’s maximum charging rate capability.
Note that this calculation is theoretical and assumes ideal conditions. In practice, factors like the efficiency of the charging process and any limitations from the battery management system can affect the actual charging time.
💸 What is the cost of charging an electric car?
The cost of charging an electric car mainly lies between 6 factors:5
- Country of charging: the cost of electricity varies from country to country, influenced by local energy prices and the availability of electricity
- Type of charger (AC or DC): AC chargers are typically slower but less expensive, while DC fast chargers offer quicker charging at a higher cost. Time is money
- Charging location: charging at a highway station often incurs a higher cost compared to charging at home or at stations in urban areas
- Charging fee: some charging stations impose a standard fee for using their services. This fee is applied regardless of the amount of electricity consumed during the session
- Duration: the time spent charging the vehicle, sometimes, also factors into the cost
- Unplugging time: to avoid the issue of charging station occupied by 100% charged vehicles, some providers use a flat tax or fee per minute for the time a car remains plugged in after it is fully charged
Based on our experiences and considering the various factors previously mentioned, the cost for a full charge of an electric car in Europe typically ranges between $10 to $30.
⚡ When will electric cars become more affordable?
Electric cars are expected to become more affordable as the technology used in their production becomes less expensive. This process involves advancements in battery technology, economies of scale as production increases, and more widespread adoption of electric vehicles. However, keep in mind that actual battery technologies (Li-ion) and some motors mostly use rare, raw materials. These materials, often scarce and expensive to extract and process, contribute significantly to the overall cost of the batteries and, by extension, the electric vehicles themselves.
References
- Bosch Mobility, “Electric motors and active parts”, Bosch, https://www.bosch-mobility.com/en/solutions/electric-motors/electric-motors-and-active-parts (accessed 17 December 2023) ↩︎
- EV Database, “Tesla Model 3 Long Range Dual Motor (2023) price and specifications – EV Database”, EV Database, 2023, https://ev-database.org/car/1992/Tesla-Model-3-Long-Range-Dual-Motor (accessed 17 December 2023) ↩︎
- EV Database, “Skoda Enyaq 85 (2023) price and specifications – EV Database”, EV Database, https://ev-database.org/car/2020/Skoda-Enyaq-85 (accessed 17 December 2023) ↩︎
- Bosch Mobility, “Regenerative braking systems”, Bosch, https://www.bosch-mobility.com/en/solutions/driving-safety/regenerative-braking-systems (accessed 17 December 2023) ↩︎
- Ionity, “How much does it cost to charge at IONITY?”, IONITY, 2023, https://support.ionity.eu/en/payment-billing/how-much-does-it-cost-to-charge-at-ionity (accessed 17 December 2023) ↩︎