Advanced lead-carbon batteries could enable 48V super hybrid vehicles
Advanced lead-carbon batteries could attract the interest of carmakers since they enable them to introduce mild hybrid powertrains based on the new 48V supply network and thus at low additional cost, believes EALABC project coordinator Allan Cooper. "This will help them comply with stringent CO2 regulations being introduced in 2020 with even tougher rules following in 2025", he said. What’s more, these batteries are made of materials that can be fully recycled into new batteries, enabling OEMs to further reduce their emissions. "This provides the most cost effective solution for 48V hybrids, which have a unique requirement for a battery demanding a high rate partial state-of-charge (HRPSoC) capability," Cooper explained.
Another advantage of advanced lead-carbon batteries: They can be charged at temperatures of minus 30 degree Celsius (-22°F) – a temperature range in which lithium-ion batteries already exhibit significantly lower performance than at normal temperatures. This temperature stability is essential for vehicles to be driven in the "snow-belt" countries in Europe, the northern part of the United States and Canada. Unlike their lithium-ion counterparts, advanced lead-carbon batteries do not require active cooling even at normal and high temperatures and no expensive battery management system.
“Future battery developments will most likely combine advanced lead-carbon electrochemistry with other types of battery design with for example bipolar technology, which will reduce the lead content by as much as 40 per cent, substantially reducing the size of a 1 kWh battery required for mild electrification of the powertrain,” says Cooper. “Meanwhile, advanced lead-carbon batteries, with their high levels of carbon in the negative active mass, already represent an exciting development that is truly state of the art, resulting in much improved battery performance ideally suited to 48V hybrids.”
The additional functionality of a 48 V hybrid vehicle fitted with a Belt Integrated Starter Generator (BISG), compared with simple 12 V stop-start systems, typically includes torque assist as well as kinetic energy recovery. This is achieved effectively using electronically controlled switched-reluctance motor-generators, which avoid the need for rare earth permanent magnets. These compact electrical machines can be rated up to 12.5 kW in a package little larger than a conventional alternator. Connected to the powertrain belt system, they avoid the cost and complexity of directly driving the road wheels.
In this context, the EALABC (the European arm of the US-based ALABC, an R&D organisation based in North Carolina), also promotes the UltraBattery, a hybrid energy storage devices developed by Australia-based Commonwealth Scientific and Industrial Research Organisation (CSIRO). This battery type combines ultra-capacitor technology with lead-carbon electrochemistry in a single cell with a common electrolyte. The result is an economical, fast-charging and discharging battery with high power and a long life, and can be made using existing manufacturing facilities.
“With further development of 48V powertrain technology, we anticipate being able to reduce CO2 emissions by as much as 30 per cent compared with today’s baseline,” says Cooper. “Moreover, the low additional cost of €50-60 for each 1 % of CO2 reduction achieved is as little as one-tenth the premium of high voltage (200-400V) hybrids and pure battery electric vehicles – which presently are deemed unaffordable by the average motorist.”
Further information: www.alabc.org.