The main objective of the ECLIPSE project is to demonstrate the feasibility of the optimised Lithium-Sulphur cell technology so that it can make its way towards space applications. Using a new battery technology on a satellite or a launcher is only possible once it has been successfully demonstrated on three main levels: at cell, at battery and at system level.
All three levels will need to be successfully tested in order to demonstrate the feasibility of the Li-S technology. In particular, the strategic objectives of ECLIPSE are:
- Study and develop a very high energy density and long lifetime cell by improving its four main components: anode, cathode, separator and electrolyte.
- Study encapsulation methods in order to comply with the constraints of the space environment associated with battery module designs for electrical tests.
- Assess the impacts at system level of Li-S technology: This aims at paving the way to the integration of the Li-S batteries into spacecraft systems.
In order to meet its key objectives, ECLIPSE will need to overcome challenges at cell, battery and system level:
At cell level
The first challenge with Li-S technology is linked to its cycling capability that can be limited by a phenomenon called “shuttle”, which is linked to polysulphides solubility. During charge and discharge of Li-S batteries, lithium polysulphides Li2Sn are created, which are soluble in commonly used ether-based electrolytes. If the initial reaction with the lithium anode produces Li2S2 and Li2S then these substances are irreversibly deposited on the anode, causing an irreversible capacity loss. A drawback of the existing solutions developed for the shuttle phenomenon is a reduced energy density. Therefore, the challenge is to maximise the high energy density (>400 Wh/kg) offered by Lithium-Sulphur.
At battery and cell encapsulation level
Two challenges are foreseen in this field. At battery level, a prototype battery module will have to be manufactured, including a cells balancing system able to be submitted to electrical tests, in particular space cycling profiles. At cell encapsulation level, a theoretical study of a cell encapsulation concept will have to be performed in order to ensure that the requirements of space environments are met. Overcoming these challenges will significantly aid in the preparation of a roadmap for the deployment of Li-S technology for space applications.
At system level
Numerous tasks will have to be completed successfully at the system level in order to meet the ECLIPSE objectives. These consist of the elaboration of an electrical model of the cell that takes into account ageing effects, the detailed cell design, the experimental results and the assessment of system-level impacts while accommodating Li-S batteries within spacecraft and launchers. The electrical model could be used for system level analyses such as the definition of control laws for space battery management systems or space power subsystem sizing.