Battery technology

[adapted from Torqeedo website]

High-performance and safety: Torqeedo LIMA cells

Lithium-based battery systems are by far the most powerful energy carriers currently available. On the one hand they are  characterized by a high specific energy density. This means that they are able to store a large amount of energy per kilogram of battery weight. In addition, lithium batteries can withstand high current: in other words, they are able to deliver their capacity even under high loads. Both of these characteristics are of great importance for applications in boat drives: on the one hand, the battery weight and volume on board is reduced. On the other hand, the lithium-based battery systems ensure that the power supply does not collapse even when the boat‘s electro-motors temporarily draw high currents from the batteries.

An additional advantage: lithium batteries do not display a memory effect and are cyclically stable. Even when stored for many months, almost no charge is lost, in contrast to  conventional lead batteries.

Torqeedo batteries are also extremely robust and are secured against incorrect handling. In addition, they are protected against short-circuiting, overvoltage and excessive discharge.

The high energy density of lithium cells demands effective safety technology. For this reason, Torqeedo uses exclusively lithium-manganese safety cells. These so-called LIMA cells offer the highest safety standard of all lithium-based batteries: Only LIMA cells are able to master the necessary safety tests even when the safety electronics are switched off. These safety tests include in particular:

  • Crash tests: a fully-charged battery is crushed with a ten-ton hydraulic press
  • Nail tests: a nail is hammered right through the case of a charged battery until it comes out of the other side. This leads to the maximum possible number of battery cells being short-circuited.
  • Overcharge tests: the battery packs are overcharged with 42 V at 7.5 A until the cells are destroyed.
  • Short-circuit tests: the main contacts are short-circuited without the safety circuit.
  • High-temperature tests: the aforementioned tests are undertaken on a 300° F pre-heated battery.

Alternative lithium battery concepts in round cell format or in lithium polymer packs (“Li poly”) do not fulfill these criteria due to the chemical composition of the battery (cobalt or nickel cathode). Additionally, in case of a fault such as, e.g. short-circuit, overload, mechanical damage, lithium polymer packs react in a highly critical manner due to the missing safety mechanisms immanent within the cells.

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