Silicon-based titania coated anodes for lithium-ion capacitors

Abstract

Lithium-ion capacitors are promising energy storage devices aiming to bridge the performance differences between battery’s energy density and capacitors power density. In this project we aim to bypass the inconvenient process of pre-lithiating the anode in LICs, by using atomic layer deposition (ALD) grown titania (TiO2) grown on Si-electrodes Different coating thicknesses of TiO2 was tested to show their effect on the performance of the cells. The electrodes of Si and Si@TiO2 were tested in half cells using Li-metal as counter electrodes. As cathodes for full cells, activated carbon (AC) electrodes were used due to their high surface. The capacity of Si@TiO2 electrodes with 5 and 8 nm coatings of TiO2 were measured to be stable at 13.3 and 45.2 μAh/cm2, after 5000 cycles at 34 μA/cm2. AC|Si@TiO2 full cells with coatings of 5 and 8 nm showed a capacity of 350 μAh/cm2 at currents of 17 μA/cm2 and 50 μAh/cm2 at currents of 34 μA/cm2. The samples stabilized at 13 and 17 μAh/cm2 for currents of 340 μA/cm2. The full cells showed great capacity retention and no capacity degradation after rate capability tests. With the use of cyclic voltammetry, the means of storage was determined for both half cells and full cells fabricated in this project. The first half cells of Si|Li have Faradaic charge transfer through redox reactions, as is known for LIBs. For the full cells of AC|Si@TiO2 they initially show Faradaic charge transfer through redox reactions before shifting to pseudocapacitive mechanisms as known for SCs.