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As part of the TIETeK project run by Fraunhofer-Gesellschaft e.V., one of the many cell construction technologies available to CCI was used to build an energy-storage system for the primary supply of the deep-sea robot shown below. The lithium accumulators, the battery management system and the modular structure were designed so that pressures of up to 600 bar (corresponding to an operating depth of approx. 6000 m) acting on the system as a whole would not affect functionality. This application-specific characteristic meant the AUV (autonomous underwater vehicle) could be built to be pressure-tolerant, which brought with it major advantages in terms of manufacturing and costs. The AUV was designed for deep-sea resource exploration. The CCI’s preferred development partner, the Fraunhofer Institute for Silicon Technology, was responsible for developing the energy-storage system and designing the prototype vehicle.
The construction concept of the TIETeK AUV is modular, all other modules – such as sensors, actuators, drive train and communications equipment – having been developed and built by other development partners.
The energy supply is provided by four energy-storage systems connected in series. The individual modules consist of 12 cells and are connected with hermetically sealed cable plug connections. To achieve the desired pressure tolerance, the modules are surrounded by seawater so that the ambient pressure is transmitted to the energy-storage systems. The individual modules were tested at hydrostatic pressures of up to 600 bar and optimised for ambient temperatures of between 0°C and 50°C.
The pentagonal geometry of the module utilises the space available more efficiently than conventional designs. Such a configuration gives a higher energy and power density at module level and also has a positive effect on the AUV’s centre of gravity. The encapsulated BMS is visible in the image.
CCI’s cell construction technology fulfilled the requirement profile optimally, which meant achieving very high energy density and uniform power output and consumption, combined with moderate temperatures. We were also able to satisfy the need for a modern combination of high-energy materials for anode and cathode thanks to our outstanding coating technology for the manufacture of electrode foils and a flexible method of cell construction.
The test criteria used include the voltage requirements and the resulting capacities in charge and discharge tests for different performance profiles. Cycle stabilities, temperature testing and life testing serve to characterise the cell properties, some of which are given below:
- 20 Ah cell capacity (0.1°C, room temperature)
- 3.7 V nominal voltage
- 4.2 V max. charge voltage
- 3.0 V min. discharge voltage
- 160 Wh/kg grav. energy density
- 370 Wh/l vol. energy density