Electrochemical Lithiation of Ge: New Insights by Operando Spectroscopy and Diffraction

Abstract

The relatively high cost of metallic germanium (Ge) as a lithiumion battery negative electrode material is more than counterbalanced by its high capacity, high lithium diffusivity, and electronic conductivity. Using a unique and highly complementary set of operando characterization techniques, we propose a complete mechanism for the reversible lithiation of Ge. The electrochemical mechanism is found to be determined by the process of discharge/charge: (i) independent of the charge/discharge rate amorphous a-LiGe is proposed as the first intermediate during the lithiation of c-Ge, followed by Li 7 Ge 3 , and (ii) at low potential Li 15 Ge 4 is observed, but only for moderate rates and never at low rates, where indeed an "overlithiated" phase is preferred. The complementarity of the data obtained from XAS, Raman spectroscopies, and XRD, all in operando mode, was crucial in order to understand the complex mechanism based on reversible formation of the various crystalline and amorphous phases.

Towards Germanium Layered Materials as Superior Negative Electrodes for Li‐, Na‐, and K‐Ion Batteries

“…Secondly, recent studies indicate that Ge is particularly sensitive to the cycling conditions and parameters such as C/rate, morphology or electrode formulation can influence the type of phases that are formed. For instance in one of our previous studies for the lithiation of Ge, it was found that the cycling at relatively slow regime permits the stabilization of Li 17 Ge 4 , a more lithiated phase than Li 15 Ge 4 . Another study concerning the sodiation of Ge Nanowires, has shown the formation of Na 1.6 Ge, much sodiated phase than the expected NaGe .…”

Chemical and Electrochemical Lithiation of van der Waals Tetrel‐Arsenides

“…Equations (3) and( 4) assume that SiAs or GeAs is converted into the highest reported Li-Si(Ge) binaryp hase and the most commonly accepted form of lithium arsenide. [43][44][45][46][47][48][49][50] GeAs þ x Li ! Li x GeAs ð182 x mAh g À1 Þ ð1Þ…”

Cobalt Carbodiimide as Negative Electrode for Li‐Ion Batteries: Electrochemical Mechanism and Performance

“…Full delithiation was enforced by holding the potential at 3 V at the end of charge. The whole data set consisting of 126 Co K‐edge XAS spectra was treated globally using the chemometric approach already described in our previous studies . In short, the number of independent components needed to describe the whole set of spectra is first obtained by PCA, and in a second step the corresponding pure spectral components are reconstructed by MCR‐ALS algorithm by imposing physical and chemical constraints .…”