Electric vehicle batteries: explained
Most electric vehicle owners have a simple understanding of what electric vehicle batteries are: that EV batteries are the sources of power of their cars and also serve as storage for that much needed electrical energy for their next drive.
However, the “humble” EV battery is, in truth, an amazing technology that has gone through decades of evolution from powering simple gadgets like flashlights and now to electronic devices such as your smartphone and computer. Who would have thought that the EV battery can be capable of providing power to an entire vehicle?
Let us delve deeper into EV batteries by taking a closer look at the most basic elements in its hierarchy, namely EV battery cells.
What are EV batteries made of?
As mentioned in our introduction, the most basic elements in the hierarchy of EV batteries are the EV battery cells.
An EV battery cell consists of six major components, which are made out of base and precious metals and elements which enables the battery to function in its dual role as power provider and energy storage. Listed below are the major EV battery components and what they are made of:
- Anode – Graphite
- Cathode – Aluminum, nickel, manganese, cobalt, iron, lithium
- Separator – A micro-porous polymer called polyolefin
- Electrolyte – Lithium hexafluorophosphate
- Current collectors – Aluminum, copper
- Casing – Aluminum, steel
EV battery design hierarchy: key elements
All EV batteries have a unique EV battery design, the key elements of which form a distinctive design hierarchy. These key elements are:
- Individual EV battery cell – This is the smallest and most basic packaged form of the battery. At present, EV batteries contain units of Lithium-ion cells delivering one to six volts per cell.
- Modules – Here, the cells are connected together in parallel or series and are enclosed in a housing.
- Battery pack – The final, deployable form of the EV battery, consisting of multiple modules connected together in parallel or series, providing the required output for specific applications in the EV.
EV battery cell formats
EV battery cells come in three formats: cylindrical cells, prismatic cells, and pouch cells.
Among the EV battery cell formats, cylindrical cells are characterized by a symmetrical shape which makes them efficient to be packed together. Compared to the other EV battery formats, cylindrical cells are the least expensive to manufacture because their casing allows for superior containment and provides efficient mechanical resistance from both external and internal stresses.
Prismatic cells are much larger than cylindrical cells. Enclosed in a hard, robust casing of welded aluminum or steel, these EV batteries are capable of providing more power and store more energy. In addition, the casing design provides improved heat management compared to cylindrical cells. While the cell used in electric car batteries manufactured in China are primarily prismatic (largely because of their preferred cell chemistry of lithium iron phosphate), the main drawback to this cell format is that they are expensive to manufacture.
Among the EV battery cells, pouch cells are distinctive for their unique pouch-like EV battery design. While they are similar to prismatic cells, the difference lies in their casing. Prismatic cells have a hard casing while pouch cells are contained in laminated foil or soft plastic casing. Although their packaging efficiency is higher, pouch cells have the lowest mechanical resistance, have greater vulnerability for penetration, and a higher tendency for swelling.
Most common cell chemistries in EV batteries
In an earlier section, we enumerated the metals and elements that make up EV battery cells. These main cell chemistries found in EV battery components help to identify the type of electric vehicle batteries installed in an electric car.
Lithium-ion EV batteries are the most popular batteries which can be found in majority of EVs today. Aside from their cost-efficiency, these batteries provide superior energy storage capacities. Lithium-ion batteries also come in a variety of cell chemistries. Lithium nickel cobalt aluminum oxide batteries are commonly found in Tesla Model 3 cars. However, models of these cars that are made in China utilize lithium iron phosphate battery cells.
Nickel Manganese Cobalt
Nickel manganese cobalt batteries are noted for its balanced power delivery and energy storage. These batteries can be found in Chevy Volts.
Nickel Metal Hydride
Because they were less expensive to manufacture, nickel metal hydride batteries were the cells used in the world’s first hybrid cars, among them the Prius. While lithium-ion batteries have edged out nickel metal hydride batteries, they can still be found in some hybrid EVs, a good example of which is the 2020 Toyota Highlander.
Lithium sulfur batteries can be found in EV buses because of their large energy storage capacity. The main drawback of these batteries is that they need to be sufficiently heated up before they can generate the amount of power needed by the EV to run.
Lead acid batteries are primarily used nowadays in low performance EVs, such as golfcarts. Unlike the other battery types, lead acid batteries are noted for their low maintenance and are easy to replace. However, lithium-ion batteries have outclassed lead acid batteries because of the cheaper manufacturing of the former.
EV battery safety
Electric vehicle batteries pose a risk of combustion because of its organic liquid electrolyte content. The electrolyte is made out of compounds that are noted for their volatility, corrosiveness, and flammable properties. Some of the factors that can compromise EV batteries include physical damage, the occurrence of short circuits as a result of overheating, and unreliable charging. These factors impose three potential hazards with EV battery use, namely corrosion, fire, and explosion.
EV battery manufacturers perform various compliance tests to ensure that the EV battery design – starting from the basic EV battery cells to battery modules to the final battery pack – are safe. Among the compliance tests being done on EV batteries are vibration, thermal and mechanical shock, watertight (anti-leakage) and immersion, fire resistance, and overcharging tests.
In addition, every EV battery is equipped with a Battery Management System (BMS) which monitors the battery during charging and discharging and a Battery Thermal Management System (BTMS) to control its temperature to prevent overheating.
Can you recycle EV batteries?
Despite future EV battery technology being geared towards extending the lifecycle of the battery, ultimately all EV batteries will reach the end of their lifespan. These means that strategies for the recycling and reuse of these EV battery packs should be in place. The main goal is to keep EV batteries and their chemistries out of the global waste streams to prevent negative environmental and human health impacts.
One of these measures is to ensure the manufacturing of sustainable EV batteries, using materials that can be recycled from old batteries. Under the general term of “destructive dismantling”, these recycling processes involve destroying old batteries while, at the same time, recovering the valuable materials, particularly lithium, cobalt, nickel, and aluminum.
Here are current “destructive dismantling” processes that are being done today:
- Smelting – The organic materials, including the anodes and electrolyte, are burned at high temperatures. The valuable metals are then recovered and sent to a refinery to make them suitable for reuse. Other materials, including lithium, are recycled as slag, which is used in concrete.
- Direct Recovery – This process specifically recovers all the reusable battery-grade materials. Through a complex variety of physical and chemical processes, the components are separated and the active materials are recovered. Unlike smelting, direct recovery uses low temperatures with a minimum energy requirement.
- Intermediate Processes – This process is in-between the above two processes. Intermediate processes allow for the processing of various types of batteries, not like direct recovery, and the recovery of reusable materials is greater, compared to smelting.
Electric vehicle batteries are an evolving technology. While manufacturers are working to improve on the batteries’ driving range and lifecycle, research is also being undertaken on recycling processes in order to recover precious metals and elements for reuse in new EV batteries or for other functions.