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Li Ion Battery Technology in Materials Handling

Li Ion Battery Technology in Materials Handling

Full Description

In the case of industrial applications, Li Ion battery technology can be seen in two lights, as a means of boosting the performance of existing electric drive devices that used Lead Acid batteries and as a replacement for light duty diesel or bottled gas internal combustion engine (ICE) drive trains.

Li Ion batteries do not tolerate overcharging, this can lead to cell failure or even an explosion. Li Ion cells should not be over discharged which typically means the cells should not be discharged below 15-20% of remaining capacity (dependent on chemistry and construction) as this reduces the cycle life of the battery and may lead to premature cell failure. The two previous requirements create the need for maintaining the pack in a “balanced” condition where all the cells are kept at the same state of charge (SoC)/discharge, so that individual cells do not find themselves being overcharged or discharged ahead of the rest of the pack, with the accompanying cell damage.

The high power density of lithium Ion batteries requires that care be taken in all cases. This means safety functions that monitor and protect the pack against excessive current flow and also a continuous check for the isolation to earth. Finally, there is a need for a switching circuit to connect and disconnect the battery from the load.

The issues above should be controlled by the battery management system, which provides all of the safety features and in addition communications interfaces for reporting the condition of the pack including cell voltages and temperatures, state of charge (the percentage energy left in the pack) and state of health (the performance of the pack relative to new).

Replacing Lead Acid

After 150 years of development, lead acid still has a lot of development potential, or so some say. But as it stands now, Li Ion, with three times the energy density and between three and five times the cycle life of a maintenance free, VRLA battery, the only real card Lead Acid has to pay is price. Even this thin advantage is eroding as Li Ion gets cheaper and the life cycle advantage gets taken into account.

The case for lead acid weakens further when low temperatures are involved such as in a cold room, here the energy content of the battery may be as little as 20% of the capacity and room temperature, Li Ion would typically be at least 70%.

Batteries in more detail

Li Ion batteries represent a family of chemistries typically relating to the cathode chemistry and in the case of Titanates, the anode. The different chemistries have different characteristics and costs that make them suitable for different applications.

For industrial applications, FePO4 is the favoured for cost and safety reasons, as it is not susceptible to thermal runaway and does not include expensive cobalt as part of its cathode. Hardcase, prismatic, large format batteries with costs of around €0.50/Wh are now readily available. When combined with a suitable battery management system, these batteries are already capable of competing favourably with Lead Acid when viewed on a lifetime costs basis.

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