Their low cost and ability to start the engine at cold temperatures sets them apart in conventional and basic micro-hybrid vehicles, and as auxiliary batteries in all other automotive applications, according to the report.

With regard to overall storage capability and potential for further fuel efficiency improvements, the demand for larger battery systems based on lithium, nickel and sodium will continue to grow through the increased market penetration of vehicles with higher levels of hybridization and electrification.

In any automotive application, regulatory decisions to phase out established battery technologies would impact negatively on overall vehicle performance and cost, according to the report.

The study reaches this conclusion through a detailed analysis of the technical requirements placed on the battery in three different classes of conventional, hybrid and electric vehicles, together with an explanation of which technologies are able to fulfill them.

Currently all battery technologies have specific performance profiles that serve a well-defined purpose in automotive applications and continue to have an irreplaceable role in reducing CO₂ emissions from transport. In particular, this report demonstrates the necessity of maintaining the exemption for lead-based batteries within the EU End of Life Vehicle Directive’s wider ban on lead in light-duty vehicles. The EU’s legislative and regulatory framework should guarantee a fair and technology-neutral competition between battery technologies.

—EUROBAT chairman Johann-Friedrich Dempwolff

The report also makes clear that a transition towards other battery types would have significant ramifications for development times and would be expensive to implement effectively. In order to optimise fuel efficiency improvements in each vehicle type, automobile manufacturers need the flexibility to choose the most appropriate batteries from a technical and economic perspective.

The examined the performance profiles of the automobile battery technologies currently in use in three vehicle classes:

1. Conventional vehicles, including start-stop and basic micro-hybrid vehicles are equipped with a 12V lead-based battery, which is required to start the engine and supply the complete electrical system, and can also be expected to provide start-stop functionality, as well as the entry class of braking recuperation and passive boosting.

   Due to their excellent cold-cranking ability, durability and low cost, 12V lead-based batteries remain the only battery technology tested for the mass market that satisfies the technical requirements for these vehicles. This is expected to be the situation for the foreseeable future, according to the report.

   Advanced lead-based batteries (AGM and EFB technologies) are installed to meet extra requirements in start-stop and basic- micro-hybrid vehicles, due to their increased charge recoverability and higher deep-cycle resistance. In these applications, they are currently 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.

2. Hybrid vehicles, including advanced micro-hybrid, mild-hybrid and full-hybrid vehicles rely on the battery to play a more active role, with the energy stored from braking used to boost the vehicle’s acceleration. In full-hybrid vehicles, the stored energy is also used for a certain range of electric driving.

   Several battery technologies are able to provide these functions in different combinations, with nickel-metal hydride and lithium-ion batteries preferred at higher voltages due to their fast recharge capability, good discharge performance and lifetime endurance. At high voltages, lead-based batteries are so far limited by their more modest recharge and discharge power and capacity turnover.

   Although nickel-metal hydride batteries have been the predominant battery technology for full-hybrid vehicles, the decreasing costs of lithium-ion systems continue to improve their competitiveness.

   These vehicles also utilise a second electrical system on a 12V level for comfort features, redundancy and safety features. This electrical system is supplied by a 12V lead-based battery.

3. In plug-in hybrid vehicles and full 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 plug-in hybrid vehicles, or as the only energy source in full electric vehicles (100 km+). In plug-in hybrid vehicles, the battery must also perform hybrid functions (i.e. regenerative braking) when its capability for electric drive is depleted.

   Lithium-ion battery systems remain the only commercially available battery technology capable of meeting requirement for passenger cars according to EV driving range and time, due to their high energy density, low weight, good recharge capability and energy efficiency. Other battery technologies (nickel-metal hydride, lead-based etc.) cannot deliver the required level of performance for these applications at a competitive weight.

   For commercial applications, harsh environments and heavy duty vehicles, high-temperature sodium nickel chloride batteries are a competitive option.

4. All hybrid, plug-in hybrid and full electric vehicles also utilize a second electrical system on 12V level for controls, comfort features, redundancy and safety features. This electrical system is supplied by a 12V lead-based battery.

Market consultancy Avicienne’s 2020 projections for market development of automotive applications and their corresponding battery technologies (2013). Click to enlarge.

The report also outlines how the market may change through 2025, and how individual battery technologies may continue to develop.

• Lead-based batteries. For technical and socioeconomic reasons, 12V lead-based batteries will continue to be the essential mass-market system in Class 1 vehicles for the foreseeable future (and as auxiliary batteries in Class 2 and 3 vehicles).

  By 2025, lead-acid batteries 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 stabilisation). Therefore their cycle life, power density and charge acceptance will need to be further improved.

  European battery manufacturers are currently working to implement the following general improvements: carbon nanotechnology additives to improve the conductivity of active materials; high surface area doping materials to increase charge acceptance while avoiding hydrogen evolution (gassing); low-cost catalysts to recombine hydrogen and oxygen produced at regenerative brake events; and light-weighting solutions.

  Lead-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 lead-based batteries and other technologies at different voltages will also see accelerated commercialisation in the next decade.

  A dual board-net allows for batteries of different voltages to be integrated in vehicles, without having to change the voltage of on- board electronics. 48V/12V systems are beginning to be considered for increasing fuel efficiency in micro- and mild-hybrid vehicles. Such a configuration involves a conventional 12V network using a lead-based battery, but adds an additional 48V network powered by a 48V battery (lithium-ion, lead-based etc.). The maximal charge voltage (of the legal limit of 60V) is still being defined by OEMs.

• Nickel-metal hydride batteries. Although nickel-metal hydride 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 lithium-ion batteries.

• Lithium-ion batteries. Significant resources will continue to be spent on improving the performance, cost, systems integration, production processes, safety and recyclability of high-voltage lithium-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 lithium-ion batteries in other applications. It is expected that by 2025, lithium-ion batteries will be implemented in some 48V dual-battery systems together with a 12V lead-based battery to further increase fuel-efficiency in advanced micro-hybrid and mild-hybrid vehicles.

• Sodium-nickel chloride batteries. The report also suggests that sodium-nickel chloride 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, cost, systems integration, production processes and safety parameters for sodium-nickel chloride batteries. Power density, cycle life, energy density and reliability are all expected to be improved by 2025, with overall cost to decrease significantly.

The report was drafted by all battery manufacturing member companies of EUROBAT’s Automotive Batteries Committee (Johnson Controls EMEA, EXIDE Technologies, FIAMM, SAFT, Moll Batterien, Banner Batterien, Dow Kokam, S.C. Rombat, and Inci Aku). It was then extensively reviewed and endorsed by members of the International Lead Association (ILA), European Automotible Manufacturers Association (ACEA), Japanese Automobile Manufacturers Association (JAMA) and Korean Automobile Manufacturers Association (KAMA).

Resources

• A Review of Battery technologies for Automotive Applications