Operando X-ray Studies of Crystalline Ge Anodes with Different Conductive Additives

There is limited understanding of the lithiation reaction mechanisms for crystalline Ge and the effects of various battery components, including conductive additive type, on Ge transformations into amorphous and crystalline phases during electrochemical charge and discharge processes. In this work, we study the dependence of the phase transformations of crystalline Ge anodes on two common carbon-based conductive additives used in lithium-ion battery electrodes through operando X-ray diffraction and X-ray absorption spectroscopy. We find that Ge electrodes using carbon nanotubes as conductive additives exhibit higher structural and electrochemical reversibility compared with those with carbon black additives as well as better stability in cycling. On the basis of this, a proposed strategy to prolong the cycle life of crystalline Ge anodes is presented. Our operando XRD and XAS results show how the reaction pathways (phase transformations and local structural changes) of Ge anodes depend on conductive additive and impact the battery cycling performance.