Abstract
Nowadays, the batteries play a key role in almost all of the technologies that surround human kind. In order to satisfy the increasing demand, the design of more efficient devices with higher energy density and cycle life is crucial. In this context, silicon and germanium appear as promising candidates for electrode materials due to their high theoretical capacities. Although, prior to the implementation of these materials at an industrial level, several challenges must be addressed. The high delivered capacities come at the expense of a volume expansion and contraction upon alkali insertion and deinsertion. These volume changes in the Si and Ge particles, lead to particle pulverization, detachment from the current collector, excessive and uncontrolled formation of SEI layer and eventual capacity fade. Different strategies have been reported in the literature to overcome the aforementioned challenges. In this work, two approaches are considered, the study of the Si1-xGex alloys and the use of a layered morphology. In the first one, the formation of the Si1-xGex solid solution improves the capacity retention and the electronic conductivity. In the second one, the layered Siloxene and germanane, derived from the CaSi2 and CaGe2 Zintl phases buffers the volume changes and improves the kinetics of the system. On the other hand, the fundamental study of their electrochemical mechanism is crucial to understand the reasons behind an improvement and a failure. Thus, in this work we have studied the electrochemical lithiation mechanism of the Si- and Ge- based materials in an attempt to identify the different phases that are formed during cycling