Team seeks to extend battery life in all-electric locomotive

Penn State University researchers are developing more cost-effective ways to prolong the life of batteries in an experimental all-electric locomotive.

The locomotive, Norfolk Southern Railway No. 999, is the first all-electric, battery-powered locomotive in the US and employs 1,000 lead-acid batteries.

The experimental locomotive’s batteries are, however, finitely rechargeable and the locomotive shuts down when one battery fails.

According to Penn State, a leading cause of damage in lead-acid batteries is sulphation, a degradation of the battery caused by frequent charging and discharging that creates an accumulation of lead sulphate.

In a recent study, the researchers looked for ways to improve regular battery management practices.

The methods had to be non-destructive, simple and economical, using as few sensors, electronics and supporting hardware as possible while still remaining effective at identifying and decreasing sulphation.

‘We wanted to reverse the sulphation to rejuvenate the battery and bring it back to life,’ said Christopher Rahn, professor of mechanical engineering.

Rahn, along with mechanical engineering research assistants Ying Shi and Christopher Ferone, cycled a lead-acid battery for three months in the same way it would be used in a locomotive.

They used electroimpedance spectroscopy and full charge/discharge to identify the main ageing mechanisms.

Through this, the researchers identified sulphation in one of the six battery cells.

They then designed a charging algorithm that could charge the battery and reduce sulphation but that was also able to stop charging before other forms of degradation occurred.

The algorithm revived the dead cell and increased the overall capacity. The researchers, who reported their results in the current issue of Journal of Power Sources, then compared the battery with a new battery.

‘We desulphated it and we increased its capacity,’ said Rahn in a statement. ‘We didn’t increase it all the way to brand new. We weren’t able to do that, but we did get a big boost.’

The researchers increased the cell capacity by 41 per cent and the overall battery capacity by 30 per cent.

Even better results might have occurred if sulphation were the only ageing mechanism at play, but the researchers found that other factors reduced capacity as well.

‘Some of the other cells we identified may have had a water-loss issue,’ said Rahn. ‘And for these types of batteries, there’s nothing you can do about it.’

Other mechanisms that can damage lead-acid batteries include positive electrode corrosion, irreversible hard sulphation, positive electrode softening or shedding, electrolyte stratification, internal short circuiting and mechanical damage.

The researchers are now developing alternative models to replace the electroimpedance spectroscopy model that would allow charging right up to, but not past, sulphation in batteries where sulphation is not yet present, with the aim of preventing it from occurring in the first place.