Continuous Hydrothermal Synthesis of Metal Germanates (M2GeO4; M=Co, Mn, Zn) for High-Capacity Negative Electrodes in Li-Ion Batteries

摘要

Nanosized metal germanates (M2GeO4; M=Co, Mn, Zn) are synthesized using a continuous hydrothermal flow synthesis process for the first time. The electrochemical properties of all samples as active materials for negative electrodes in Li-ion half cells are explored. The galvanostatic and potentiodynamic testing is conducted in the potential range of 3.00-0.05V versus Li/Li+. The results suggest that both alloying and conversion reactions associated with Ge contribute to the stored charge capacity; Zn2GeO4 shows a high specific capacity of 600mAhg(-1) (ten cycles at 0.1Ag(-1)) due to alloying and conversion reactions for both Ge and Zn. Mn2GeO4 is studied for the first time as a potential negative electrode material in a Li-ion half cell; an excellent specific charge capacity of 510mAhg(-1) (10 cycles per 0.1Ag(-1)) is obtained with a significant contribution to charge arising from the conversion reaction of Mn to MnO upon delithiation. In contrast, Co2GeO4 only shows a specific capacity of 240mAhg(-1), after ten cycles at the same current rate, which suggests that cobalt has little or no benefit for enhancing stored charge in germanate.