Electric Vehicles and Battery Chemistry

Electric Vehicles and Battery Chemistry An electric motor, commonly known in battery electric vehicles (BEV), replaces the internal combustion engine in fully all-electric vehicles. The vehicle's electric motor operates with a large traction battery pack, which must be connected to a wall outlet or charging apparatus, also referred to as an Electric Vehicle Supply Apparatus (EVSE). Because these vehicles are electric, they contain no conventional liquid fuel components such as an exhaust pipe, fuel tank, fuel line or fuel pump.  

Basic Components of an All-Electric Vehicle

• Auxiliary Battery (Battery - Auxiliary): The auxiliary battery provides power to the vehicle's accessories in an electrically powered vehicle. • Charge Port: The charge port enables the vehicle to connect to an external power source to charge the traction battery pack. • DC/DC Converter: This device converts the high-voltage DC power from the traction battery pack to the low-voltage DC power needed to operate vehicle accessories and recharge the auxiliary battery. • Electric Traction Motor: This motor uses power from the traction battery pack to move the vehicle's wheels. Some vehicles use motor generators that perform both driving and regeneration functions. • Onboard Charger: Receives incoming AC electricity supplied through the charge port and converts it to DC power to charge the traction battery. It also communicates with the charging equipment and monitors battery characteristics such as voltage, current, temperature and charge status while charging the pack. • Power Electronics Controller: This unit manages the flow of electrical energy delivered by the traction battery by controlling the speed and torque produced by the electric traction motor. • Thermal System (Cooling): This system maintains the proper operating temperature range for the motor, electric motor, power electronics and other components. • Traction Battery Pack: Stores electricity for use by the electric traction motor. • Transmission (Electric): The transmission transfers mechanical power from the electric traction motor to move the wheels. EV (Electric Vehicle) An Electric Vehicle (EV) is a fully electric vehicle with rechargeable batteries. These batteries are charged from the grid and, as there is no fuel tank, serve as the sole power source for the vehicle. These vehicles are also known as BEV (Battery Electric Vehicles).

HEV (Hybrid Electric Vehicle)

In a standard fuel-powered vehicle, energy from braking is lost as heat. Hybrid Electric Vehicles operate on both electricity and fuel. The energy powering their batteries is obtained through regenerative braking or during driving using an internal combustion engine. These types of electric vehicles cannot be charged by plugging them in.

PHEV (Plug-in Hybrid Electric Vehicle)

A PHEV has both an internal combustion engine and an electric motor. Like a standard hybrid, PHEVs can charge their batteries through regenerative braking or with a motor. The difference between HEVs and PHEVs is that PHEVs have a charge port. In this way, a PHEV can operate more like an EV, and when its battery is depleted, it can be charged from the grid or the internal combustion engine can come into play. PHEV batteries generally have higher capacity than HEV batteries.

Most Commonly Used Battery Chemistries in Electric Vehicles

The chemistry of a battery cell is a mixture of materials in the battery that enables electron transfer between two electrodes (anode and cathode) to achieve the desired electrical potential. Electrons flow from one electrode to the other and vice versa. Many different chemical techniques exist in this field, and each uses different materials with different costs. The chemistry of the cell has a major impact on battery cost. As the battery is the most expensive component in an electric vehicle, it plays an important role when it comes to minimizing production costs.

Types of Energy Storage Systems

The following energy storage systems are used in fully electric vehicles, PHEVs and HEVs.

Lithium-Ion Batteries

Lithium-ion batteries are currently used in most portable consumer electronics such as mobile phones and laptops because of their high energy per unit mass compared to other electrical energy storage systems. They also have high power-to-weight ratio, high energy efficiency, good high-temperature performance and low self-discharge. Most components of lithium-ion batteries are recyclable, but the cost of material recovery remains a challenge for industry. Significant initiatives are underway in this area, particularly in developed countries. For example, the U.S. Department of Energy also supports the Lithium-Ion Battery Recycling Prize to develop and demonstrate profitable solutions for collection, sorting, storage and transport of used and discarded lithium-ion batteries for final recycling and material recovery. Most of today's fully electric vehicles and PHEVs use lithium-ion batteries, but their chemistry is usually different from consumer electronics batteries. Research and development efforts continue to reduce their relatively high costs, extend their service life and address safety concerns regarding overheating.

Nickel-Metal Hydride Batteries

Nickel-metal hydride batteries, routinely used in computers and medical equipment, offer reasonable specific energy and specific power capacity. Nickel-metal hydride batteries have much longer life than lead-acid batteries, are safe and resistant to abuse. These batteries are commonly used in HEVs. The main challenges with nickel-metal hydride batteries are their high cost, high self-discharge, heat generation at high temperatures and the need to control hydrogen loss.

Lead-Acid Batteries

Lead-acid batteries can be designed to be high-power, and are inexpensive, safe and reliable. However, issues such as low specific energy, poor cold weather performance and short calendar and service life limit their use. Advanced high-power lead-acid batteries are being developed, but in electric vehicles currently available on the market, they are used only as auxiliary power.

Energy Cells and Power Cells: What Is the Difference?

Batteries can be optimized to store more energy (energy cells) or provide more power (power cells). In general, it makes sense to use energy cells in larger batteries and power cells in smaller batteries. As a battery grows, total power is distributed among more cells and each cell needs to supply less power. For example, hybrid vehicles have smaller batteries and typically require power cells. Power cells allow the battery to remain small while meeting power requirements. They are also used in high-performance electric vehicles such as Formula E. In fact, they are well suited to all vehicles with low range and high power demand.

Supercapacitors and Ultracapacitors to Increase Power

Ultracapacitors store energy in a polarized fluid between an electrode and an electrolyte. Supercapacitors and ultracapacitors, as energy storage systems, are similar to batteries but not exactly the same. While batteries use chemical reactions to store energy, ultracapacitors store electrostatic charge. As the surface area of the fluid increases, energy storage capacity increases. Ultracapacitors can provide vehicles with additional power during acceleration and hill climbing and can help recover braking energy. They can also be useful as secondary energy storage devices in electric vehicles because they help balance the charging power of electrochemical batteries. Ultracapacitors have high power output and are used with batteries to increase power. They can supply large amounts of power in a short time and can do so hundreds of thousands of times without significant degradation. Ultracapacitors have very low energy density, so they do not contribute to range. However, when combined with a lithium-ion battery pack, they manage power and energy demands very well. In summary, ultracapacitors are ideal for high power, batteries for long distances.

Battery Recycling

Since electric vehicles are a relatively new technology, only a small portion are approaching the end of their service life. As electric vehicles become more widespread, the battery recycling market will expand. Widespread battery recycling will prevent dangerous materials from entering the waste stream both at the end of the battery's service life and during production. Material recovery from recycling will reintroduce critical materials into the supply chain and increase local sources for such materials. Work continues on developing battery recycling processes that minimize the impacts of lithium-ion and other types of batteries used in vehicles on their service life. However, not all recycling processes are the same and require different separation methods for material recovery, among which the following methods stand out. Smelting: Smelting operations recover base elements or salts. These operations now work at large scale and can accept many types of batteries including lithium-ion and nickel-metal hydride. Smelting takes place at high temperatures where organic materials, including electrolyte and carbon anodes, are burned as fuel or reducer. Precious metals are recovered and sent for refining to make the product suitable for any type of use. Direct Recovery: Some recycling processes directly recover battery-grade materials. Components are separated through various physical and chemical processes and all active materials and metals can be recovered. Direct recovery is a low-temperature process requiring minimal energy. Intermediate Processes: A third type of process falls between these two extremes. Unlike direct recovery, these types of processes can accept multiple types of batteries and recover materials more efficiently throughout the production chain than smelting techniques. The separation process of different types of battery materials generally presents a barrier to recovering high-value materials. Therefore, battery design that considers disassembly and recycling is important for electric-powered vehicles to be successful from a sustainability perspective. Standardization of batteries, materials and cell design will also make recycling easier and more cost-effective. Compiled and translated by: B. Serhat Cengiz References: • https://afdc.energy.gov/vehicles/how-do-all-electric-cars-work • https://www.edfenergy.com/energywise/how-do-electric-cars-work • https://afdc.energy.gov/vehicles/electric_batteries.html • https://www.arenaev.com/ncm_nca_lfp_solidstate__ev_battery_chemistry_explained-news-343.php • https://www.laserax.com/blog/ev-battery-cell-types • https://www.euronews.com/my-europe/2023/03/28/in-win-for-germany-eu-agrees-to-exempt-e-fuelsfrom- 2035-ban-on-new-sales-of-combustion-en • https://www.midtronics.com/blog/what-is-the-battery-differences-in-ev-hev-phev/ • Images: https://pixabay.com/