Leading scientists describe the automotive future

“Over the past 25 years, the auto industry has reduced its greenhouse gas emissions by 20% from a 1990 baseline, less than 1% a year,” says Patrick Moseley, President Emeritus, Advanced Lead-Acid Battery Consortium (ALABC). “Over the next 35 years, the industry will have to sustain the 2-3% annual reduction that it is now achieving.”

Moseley’s co-authors are Ronald Dell, previously Head of Applied Electrochemistry, UK Atomic Energy Authority and David Rand, former Chief Research Scientist, Commonwealth Scientific and Industrial Research Organisation (CSIRO) of Australia. The first edition book focusses on road transport, a key aspect of human activity among the many sectors - including agriculture, industry and power - that require attention if sustainable development on a global scale is to be achieved.

“Our work examines the prospects for an evolution of the global transport system, which currently consumes irreplaceable resources and degrades the environment, towards one with a modus operandi that will be both supportable and benign,” comments Dell. “The global fleet of motor vehicles is now around 1.5bn, of which 1bn are cars. This is expected to reach 2bn soon after 2020, with a rapid increase in the number of vehicles anticipated in China and India”.

“Automotive manufacturers face the conflicting demands for vehicles with ever-improved performance, safety and comfort - but without any appreciable increase in cost,” says Rand. “This is being resolved through advances in vehicle design and in particular through refinement in propulsion technology. The trend is towards smaller internal combustion engines augmented by intelligent electrification with no decrease in power.”

All three authors have been involved in electrochemistry and the development of advanced battery designs and power sources, and they express their views on battery chemistries and supercapacitors being considered for use in vehicles.

“Batteries in different categories of vehicle are required to perform widely disparate duty cycles,” explains Moseley. “In a conventional internal combustion engine, the starting, lighting and ignition battery is maintained at almost a full state-of-charge of between 85 and 90%. In BEVs (Battery Electric Vehicles), the charge level of the cells declines throughout the journey from 100 to 20%, and once their chemical energy is depleted they have to be recharged for the next journey. In HEVs such as the Toyota Prius and especially the new breed of low-voltage (48V) super hybrids from Audi, Kia and other manufacturers, the batteries are subject to a critical High-Rate Partial State-of-Charge (HRPSoC) operation of 50-70%.”

The above duty cycles explain why lithium-ion batteries, with their high-voltage cells and high specific energy (W-h/kg), are currently utilised for pure electric vehicles despite their high cost and need for cooling, while the recent breakthrough of advanced lead-carbon batteries is better suited to both stop-start and 48V vehicles. The authors confirm that there appears to be little prospect in the short term of finding a battery system that can provide a BEV driving range between charges of much more than 150 miles, whilst withstanding rapid recharging for a satisfactory life and being manufactured at a competitive cost. “It could be 20 years before possible next-gen lithium-air batteries make it out of the laboratory and into the car,” predicts Rand.

“Hybrids do not eliminate tailpipe emissions, but are more fuel-efficient and, crucially, the vehicles do not suffer from the range limitations that beset BEVs,” comments Dell. “Hybrids are also in tune with progressively tighter emissions legislation, because there is a full range of designs available from the simplest stop-start and 48V forms.”

The book also refers to Rand’s involvement in CSIRO research that has contributed to the improvements gained in the performance, power capability and cycle-life of Valve-Regulated Lead-Acid (VRLA) batteries. Recently, CSIRO has provided a means for overcoming the problems of the HRPSoC duty cycle through the invention of a VRLA battery design in which the negative plate is protected from the deleterious effects of high-rate charge and discharge by sharing the current with an integrated supercapacitor. The configuration of the CSIRO UltraBattery combines a VRLA cell with an asymmetric supercapacitor in a single unit without the need for extra electronic control.

“This technology is cheaper and occupies less volume than a conventional battery-supercapacitor combination,” declares Moseley. “As part of its continuing research programme, the ALABC has fitted prototype units, made by the Furukawa Battery Company, to a Honda Insight, which successfully completed 100,000 miles at Millbrook proving ground.”

“Interestingly, an increase in the quantity of carbon in the negative active-material can promote a significant increase in battery life under HEV duty. An extensive test on East Penn’s licensed design of UltraBattery was able to reach 167,000 miles in the laboratory. The ALABC has since completed another 150,000 miles of real world driving in Arizona in a Honda Civic hybrid - a particularly demanding HRPSoC operation - and continues to run the vehicle to determine the full lifetime of the batteries. So far, they show no performance degradation and remarkably the individual battery voltages of the pack are beneficially converging as they age - though as yet we know not why.”

Several major car companies are working towards introducing lead-carbon batteries into the stop-start and 48V mild superhybrids mentioned above. Kia has announced a preference for this new battery chemistry over a lithium-ion alternative because: “lead-carbon cells require no active cooling, are more readily recycled at the end of the vehicle’s life, and can function more efficiently below 0°C.”

“For students interested in the science and engineering of the automotive sector, this is a valuable read,” said Dame Professor Julia King, Vice-Chancellor, Aston University, who was appointed in 2007 to lead a review of automotive technologies to reduce emissions. “This in-depth book provides a historical context, from the discovery and development of the steam engine and the advent of railways, through to the crucial role to be played by governments, now and over the next 35 years, if global targets for the reduction of CO₂ and NO_x emissions are to be met.”