Roll-to-Roll Electrode Processing Towards the Development of a 100 F Lithium-Ion Capacitor

Due to the advantage of combining both capacitive and faradaic charge storage mechanisms, lithium-ion capacitors (LICs) are regarded as a promising energy storage technology for many applications requiring high-power and high-energy. However, the lack of an internal source of lithium ions demands a pre-lithiation strategy for the viability of the technology. Many alternatives have shown their potential at the laboratory scale to achieve full pre-lithiation of the device, enhancing both energy and cycle life of the system. Dilithium squarate is one of those candidates. However, certain aspects are relevant to bring those strategies to real life. Thus, we aim to demonstrate this strategy at a pilot line level, by fabricating electrodes incorporating the sacrificial salt by roll-to-roll processing in a semi-automated electrode coater equipment. Moreover, to ensure a good response of the fabricated LICs under high current pulses, reducing the resistance of the cell is of high importance, and optimization of electrode processing becomes crucial at this point. In this work, the relevant aspects of the slurry formulation and roll-to-roll coating parameters of a hard carbon-based negative electrode and an activated carbon-dilithium squarate composite as positive electrode will be described. The different nature of the materials involved in both electrodes require to adapt the viscosity of the slurry, and the coating and drying parameters accordingly to ensure their correct mechanical properties. The quality of the slurry formulations is validated by the absence of agglomerates and appropriate viscosity, while the quality of final electrodes is validated by x-sectional SEM images and peeling tests. To conclude, 100 F multilayer LIC pouch cells have been fabricated. Their electrochemical characterization shows a device with low internal resistance, high capacitance, and good cycle life, confirming the good quality of the electrodes fabricated by means of roll-to-roll process.