While silicon is attractive due to its high capacity, germanium possesses a superior electronic and ionic conductivity, and is able to support much higher cycle rates. In the present paper, we investigate the electrochemical performances of Ge x Si 1−x -based electrodes with x = 0, 0.25, 0.5, 0.75, and 1. The Ge x Si 1−x samples are easily prepared by short ball milling. X-ray diffraction (XRD), Raman spectroscopy, and scanning electron microscopy−energy-dispersive X-ray spectrometry confirm that Si/Ge solid solutions are obtained with different ratios. We show that appropriate formulations of Ge x Si 1−x electrodes can produce excellent cycling performances, with an increased capacity retention compared to that of Sibased electrodes only, and with higher capacity than that of Ge-based electrodes cycled in the same conditions. For Ge 0.1 Si 0.9 , a capacity of 1138 (mA h)/g is retained after 50 cycles, and is stabilized around 1020 (mA h)/g after 100 cycles. Moreover, a limited irreversible capacity is lost on the first discharge. The electrochemical data suggest that the copresence of Si and Ge in the same phase creates a synergistic beneficial effect on the Ge x Si 1−x electrochemical performances. The electrochemical behavior of Ge x Si 1−x is investigated for the first time by in situ XRD, and an original mechanism is highlighted with the reversible formation of a new Li 15 (Si x /Ge y ) 4 ternary phase at the end of discharge. Interestingly, a decrease of the cell parameter of this ternary phase is observed continuously from the end of discharge to the beginning of charge, which might be correlated to a loss of germanium of the lithiated Li 15 (Si x /Ge y ) 4 phase.

For the first time it is demonstrated that a dense SiP2 pyrite-type obtained by a very simple ball milling method delivers outstanding capacity in both lithium and sodium batteries with up to 1000 mA h g−1 and 572 mA h g−1 sustained after 30 and 15 cycles respectively.

Nanomaterials have triggered a lot of attention as potential triggers for a technological breakthrough in Energy Storage Devices and specifically Li-ion batteries. Herein, we report the original synthesis of well-defined silicon/iron oxide nanoparticles and its application as anode materials for Li-ion batteries. This model compound is based on earth abundant elements and allows for a full investigation of the electrochemical reactions through its iron oxide magnetic phase. The elaboration of silicon with iron oxide grown on its surface has been achieved by reacting an organometallic precursor Fe(CO) 5 with Si nanopowder and subsequent slow oxidation step in air yields hollow γ-Fe 2 O 3 on the Si surface. This specific morphology results in an enhancement of the specific capacity from 2000 mAh/g Si up to 2600 mAh/g Si . Such a high specific capacity is achieved only for hollow γ-Fe 2 O 3 and demonstrates a novel approach toward the modification of electrode materials with an earth abundant transition metal like iron. This result further emphasizes the need for precisely designed nanoparticles in achieving significant progress in energy storage.