Electrochemical Sodiation and Desodiation of Gallium

Abstract

This study demonstrates the electrochemical sodiation and desodiation of gallium (Ga). A variety of techniques including galvanostatic cycling, cyclic voltammetry, as well as ex situ and in situ powder X-ray diffraction were used to determine the electrochemical reaction mechanisms. The sodiation and desodiation of Ga occurs reversibly at 0.71 V vs Na+/Na and the sodiated product was determined to be NaGa4 with a theoretical capacity of 96 mAh g−1 (567 mAh cm−3). In addition, an anomalous plateau was observed at 0.66 V vs Na+/Na during the sodiation, which was attributed to a slow diffusion of Na into Ga particles. It was also shown that Na22Ga39 was not formed even if it is one of the expected compounds from the Ga-Na phases diagram. However, new crystalline structures were observed and were attributed to metastable phases of NaGa4.