Emerging battery solutions
Published: 03 January, 2017
For decades electric vehicle fleet operators and OEMs had very little choice when it came to power sources, with batteries built using flooded lead-acid cells the only practical option. While these batteries evolved to give more power, efficiency and reliability there have always been limits to their potential. Recent innovations such as lithium-ion offer an alternative but are still relatively expensive while novel technologies such as hydrogen fuel cells have yet to find practical or affordable applications in the mass market. PWE reports.
The emergence of a new type of lead-acid battery using a technology known as Thin Plate Pure Lead (TPPL) now offers a practical and affordable alternative to conventional lead-acid and lithium-ion designs. So what are the key features and benefits of these designs and what considerations should fleet operators and OEMs make when specifying power units for their applications?
TPPL technology builds on the proven capabilities of traditional lead-acid batteries with some significant technological advances. In traditional lead-acid designs the positive and negative plates are typically over 4mm thick but with TPPL technology they are much thinner at around 1mm. More TPPL plates can therefore be fitted in any given size of enclosure which in turn increases the total surface area available. In simple terms this means more energy and more power density than conventional units of the same size. Or, put another way, batteries with the same power can be smaller and batteries of the same size can be more powerful.
The other significant difference with TPPL technology is that the conductive grid is manufactured using lead that is much purer (typically 99.99% pure) than in conventional designs. This purity results in greater stability in the chemical behaviour of the battery which improves its long-term charge acceptance and cyclic capabilities. The plates are also much less likely to corrode which means the batteries have a longer shelf-life. TPPL technology also offers extremely high recombination levels which reduces water losses during recharge which optimises battery life.
These characteristics combine to provide significant operational benefits including higher performance and the ability to charge repeatedly from any depth of discharge without affecting the condition of the battery. Moreover, the increased reliability and elimination of water loss ensures that batteries with TPPL technology is very low maintenance.
While the plates are the most significant component of the TPPL technology none of these advantages would be achieved without other materials used in the battery – particularly the electrolyte and glass microfibre separators – also being high quality. In reality the right combination and balance of plates, electrolyte and separators is needed to achieve maximum performance and reliability. Jason Mander, sales director, EnerSys UK & Ireland, says his company, in cooperation with its strategic supplier partners, has invested heavily over many years to understand and improve the technology and in the advanced techniques and quality assurance processes needed to meet these objectives.
Despite their similarities to traditional lead-acid designs, TPPL batteries both enable and require new ways of working. Typical installations will incorporate programmable chargers and a range of monitoring devices to check the status of the battery and supply the optimum amount of energy to shorten recharge times. Mander explains that EnerSys has developed a number of patented charging algorithms for its TPPL ranges for motive power and reserve power applications. These have focused on maximising the cyclic capabilities of the batteries and enabling charge and recharge from more or less any depth of discharge. Lithium-ion batteries, on the other hand, rely on conventional battery management systems which offer none of these benefits.
This has significant operational benefits for fleet operators and OEMs. First, the need to exchange a depleted battery with a fully charged replacement can often be eliminated. Instead, batteries with TPPL technology can be recharged for short periods whenever there is an opportunity, such as when an operative is on a break or completing some task away from their vehicle. In many applications this supports what amounts to continuous vehicle availability because the battery never reaches a depth of discharge low enough to require an exchange. This removes the need for expensive spare batteries or the associated handling and management infrastructure.
For OEMs, removing the need to exchange batteries and the inherent power of TPPL technology offers some interesting design flexibility. Eliminating the need to exchange batteries offers the prospect of incorporating them into designs in new ways because they no longer need to be accessible. Also, because TPPL batteries store more power than conventional alternatives, engineers have the option to specify smaller units without compromising on the overall performance of the machine.
Despite these differences, TPPL batteries have far more in common with traditional lead-acid designs than newer technologies and are probably more widely established in the marketplace. This familiarity could make TPPL more practical for operators and OEMs considering a switch from traditional lead-acid. Another subtle difference is end-of-life recyclability. Up to 90% of the materials used in lead-acid batteries, both conventional and TPPL, can be recycled. Although similar levels may be possible for lithium-ion these batteries have no intrinsic value at end of life and for the time being the recycling streams are not as established.
For further information please visit: www.enersys.com
