When it comes to the rapidly growing electric vehicle (EV) industry, the crosshairs of the materials community are focused squarely on battery technology. However, this is not the whole story. With up to 130 million battery EVs and 90 million plug-in hybrid EVs expected on the roads globally by 2030 (compared to 3 million in 2017), some big changes are on the way for some major commodity metals. What are the materials that will shape the future of EVs?
Aluminium: lightweight for long range
Aluminium has been a key metal in the development of EVs. Its low density allows for the overall vehicle weight to be reduced. This is a crucial factor for increasing the energy efficiency and thus the range of EVs. The Tesla Model S, for example, contains a whopping 661 kg of aluminium.
In the latest EV models, however, steel is winning out against aluminium for the body and chassis with the more affordable Tesla Model 3 containing around 200 kg, the VW eGolf 129 kg and the Nissan Leaf 171 kg. Despite this trend, aluminium will remain a key material for battery EVs. Added to that, huge demand is still expected from the hybrid market, where aluminium is used for the engine block and transmission.
Steel: strength and cost
Despite the low weight of aluminium, its higher cost compared to steel makes it a limiting factor when bringing down the price of EVs. In its place, advanced high-strength steels (AHSS) are being utilised for their stiffness, strength and ability to absorb energy in the event of a crash.
Due to the high strength of AHSS, the thickness of parts can be reduced, thereby keeping weight to a minimum. For example, doubling the tensile strength of the steel allows for a reduction in thickness, and therefore weight, by 30 %.
Low to high-strength steels tend to have a lower ductility as strength is increased, whereas AHSS strikes a balance between the two properties. AHSS generally have yield strengths in excess of 550 MPa, with those exhibiting a yield strength above 780 MPa being called ultra high-strength steels. The high strength allows for a reduction in the amount of material and the greater ductility for better formability.
Copper: motors and chargers
As we discussed in a previous article, copper is a major component of EVs, with the average EV containing four times as much copper as conventional internal combustion engine vehicles. This is located primarily in the motor, where it is required for rotor and stator windings.
What’s more, it is expected that the expanding charging infrastructure required for the great number of EVs will create the requirement for an additional 100,000 tonnes of copper per year by 2027.
Rare earth metals: magnets for motors
Another concept for increasing the range of EVs comes from motor technology. Some EV manufacturers such as Tesla and VW have started introducing permanent magnet motors in place of all-copper induction motors. These are more efficient and more cost-effective than motors containing only copper coils.
Concerns exist, however, about increasing incorporation of rare earth elements, such as neodymium, into EVs due to the unpredictability of its supply, 85 % of which is controlled by China.
Composites: high performance but high price
With the reduction of vehicle weight being such an important factor for increasing EV range, some suppliers are looking into composite materials for their excellent strength-to-weight ratio.
VW, for example, is using glass fibre-embedded polypropylene for the battery tray in its e-Golf. The BMW i3 and i8 both piloted the use of carbon fibre composites in EVs, with the bodies both being composed of the material.
While composites can offer an excellent strength-to-weight ratio and could potentially make up a large portion of an EV, their major limitation is the high cost compared to steel.
What does the future hold?
The two key factors determining the materials used in EVs right now are range and price. For maximising range, in terms of body materials, aluminium has been most attractive so far. Improvements in steel, however, is renewing it as a low cost, low weight favourite for EV manufacturers.
The surge in the EV market in the coming years will, in any case, mean major opportunities for the major metal commodities found these vehicles: steel, aluminium and copper.
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