3D interconnected NiSn nanowire networks for Li-ion battery electrodes

The growing demand for electrical energy storage systems caused by the energy transition and the increase of portable electronic devices puts pressure on the creation of new batteries with higher performances, longer life-time and smaller size and weight. In this context, Li-ion batteries currently appear as one of the best solutions. Indeed, thanks to the small Li ions shuttled between the electrodes of the battery, Li-ion battery can achieve high specific capacity along with long life-time. Li-ion batteries are commonly used for electric vehicles and portable electronics. In parallel to the development of batteries composition, work on the architecture can also be performed to improve the battery characteristics. Nanoscale 3D architectures are currently being developed in state-of-the-art batteries. The main goal of this master thesis focuses on the combination of a new 3D nanostructure with a promising alloy composition for anodes in Li-ion batteries. The developed anode is made of NiSn alloy (Ni3Sn4) in a shape of 3D interconnected nanowires having different diameters (230, 105 and 40nm). They are compared with 2D, i.e. films, structures and with pure Sn samples to highlight first the contribution of the 3D scale to the performances and secondly the advantage of alloyed materials (NiSn) compared to pure active material (Sn). The samples are grown thanks to cathodic electrodeposition techniques in track-etched polycarbonate templates on copper (Cu) substrates. The electrodepostion results are characterized thanks to scanning electron microscopy and energy dispersive x-rays spectroscopy. The anodes are then assembled in a "half-cell" with Li as counter electrode and are cycled galvanostatically. The surface morphology, the composition and the dimensions of the grown samples are analyzed with consideration to the parameters applied. The resulting curves of the battery cycling tests are examined and linked with the intrinsic behaviours of lithiation and delithiation upon charge and discharge but also with side mechanisms as amorphization or SEI formation. The intermediate-diameter size of nanowires (105nm-diameter) achieved the best results at low potential limitation (1V-0.01V) with a specific capacity of 1000 µA/cm² and a life cycle of 55 cycles compared to 325 µA/cm² and 35 cycles for 40nm-diameter nanowires, 750 µA/cm² during 45 cycles for 230nm-diameters nanowires and against 650 µA/cm² during 22 cycles for NiSn film. Pure Sn samples achieved higher values of specific capacity for films (1600 µA/cm²) at the expense of the life cycle of 10 cycles only. However, the deposition of Sn nanowires faced some issues and the resulting sample performances are very low and probably not representative of the real performances. The low capacity and life cycle values achieved in this study are probably due to mass loss and lack of adhesion between the deposited anode and substrate, which seem to jeopardize the samples quality. It is therefore very important to work first on this problematic to be able to analyze more accurately the developed anode performances.