Batteries For Electric Vehicles – Co-existence Of Technologies Is Needed

The various battery technologies have specific performance profiles serving a well-defined purpose in automotive applications.
Published: Wed 26 Nov 2014

Contrary to what one may expect, it is not possible to simply replace one battery type with another in an electric vehicle, without impacting on the vehicle’s performance and cost.

The reason, according to a new report from battery and automotive industry stakeholders, is that the various battery technologies – lead (Pb)-based, lithium (Li)-based, nickel (Ni)-based and sodium (Na)-based – have specific performance profiles, which serve a well-defined purpose in automotive applications and thus continue to have an irreplaceable role in reducing CO2 emissions from transport.

The report is from the Association of European Automotive and Industrial Battery Manufacturers (EUROBAT), European Automobile Manufacturers Association (ACEA), Japanese Automobile Manufacturers Association (JAMA), Korean Automobile Manufacturers Association (KAMA), and International Lead Association (ILA).

Automotive battery  market overview

The report groups the vehicle types into three classes, according to the varying demands placed on the installed batteries.

Conventional vehicles (including start-stop and basic micro-hybrid vehicles): In these vehicles, the battery is used only for starting the engine, lighting and ignition. The 12V Pb-based battery will continue to be the only viable mass market battery system for the foreseeable future due to its excellent cold-cranking ability, low combined cost and compatibility with the vehicle’s 12V electrical system.

Advanced Pb-based batteries are installed to meet extra requirements, due to their increased charge recoverability and higher deep-cycle resistance. In these applications, they again remain the only technology available for the mass market.

Vehicles in this class will continue to comprise the majority of Europe’s car parc for the foreseeable future.

Hybrid electric vehicles (including advanced micro-hybrid, mild-hybrid and full-hybrid vehicles): In these vehicles the battery is require to play a more active role, with energy stored from braking used to boost the vehicle’s acceleration. In full-hybrid vehicles, the battery system is additionally employed for a certain range of electric driving.

Nickel-metal hydride (NiMH) and Li-ion batteries are preferred due to their fast recharge capability, good discharge performance and lifetime endurance. Although the former have been the predominant battery technology for full-hybrids, the decreasing costs of Li-ion systems continue to improve their competitiveness.

These vehicles also utilize a second 12V electrical system, powered by a 12V Pb-based battery for comfort features.

Plug-in hybrid and all electric vehicles: High voltage systems of at least 15kWh are installed to provide significant levels of vehicle propulsion, either for daily trips (20-50km) in PHEVs, or as the only energy source in full EVs (100km+). In PHEVs, the battery must also perform hybrid functions (i.e. regenerative braking) when its capability for electric drive is depleted.

Due to their high energy density, fast recharge capability and high discharge power, Li-ion batteries are the only available technology capable of meeting the driving range and charging time requirements.

For commercial applications, harsh environments and heavy duty vehicles, sodium-nickel chloride (Na-NiCl2) batteries are a competitive option. NiMH batteries and Pb-based batteries cannot meet these requirements at a competitive weight.

Similar to hybrid vehicles, an auxiliary 12V Pb-based battery is installed to supply the electrical components.

Future trends in automotive battery technology

Pb-based batteries. As noted, for technical and socioeconomic reasons 12V Pb-based batteries will continue to be the essential mass-market system in conventional vehicles (and as auxiliary batteries in the other classes). By 2025, they will be expected to provide extra services in micro-hybrid vehicles to increase the internal combustion engine’s fuel efficiency (i.e. stop-in-motion, voltage stabilization). Therefore, their cycle life, power density and charge acceptance will be further improved.

Pb-carbon batteries are expected to be commercialized in the near future, and will provide high performance in terms of charge acceptance and their ability to operate at partial states of charge in start-stop and micro-hybrid vehicles.

Dual batteries using Pb-based and other technologies at different voltages will also see accelerated commercialization in the next decade.

NiMH batteries. Although NiMH batteries have been an important technical resource in the rise of hybrid and electric vehicles, their potential for further market penetration is limited by the increased performance and reduced cost of Li-ion batteries.

Because they have already reached a high degree of technological maturity, limited improvements are expected between now and 2025.

Li-ion batteries. Significant resources will continue to be spent on improving the performance and usability of high-voltage Li-ion battery systems for hybrid and electric applications. Large performance and cost improvements will be made through developments in cell materials and components (i.e. anode, cathode, separator and electrolyte). Lower cost cell design is expected by 2025, along with improvements in materials properties and the gradual scaling up in production of large cell formats.

These improvements will increase the competitiveness of Li-ion batteries in other applications. It is expected that by 2025, Li-ion batteries will be implemented in some 48V dual-battery systems together with a 12V Pb-based battery to further increase fuel efficiency in advanced micro-hybrid and mild-hybrid vehicles.

Na-NiCl2 batteries. In the coming years, Na-NiCl2 batteries will be increasingly used in the automotive market for traction purposes in heavy duty plug-in hybrid and electric vehicles.

Manufacturers will work to improve the performance and usability of Na-NiCl2 batteries. Power density, cycle life, energy density and reliability are all expected to be improved by 2025, with overall cost to decrease significantly.

In conclusion, the report advocates for the fair co-existence of battery technologies on the market. Where substitution between technologies is possible, this should be left to the application manufacturers, so they can choose the most suitable batteries for their products. As such, the legislative and regulatory framework should guarantee a fair competition between battery technologies.

Further reading

EUROBAT: A Review of Battery Technologies for Automotive Applications