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

Bauer, Dustin; Ashton, Thomas E.; Groves, Alexandra R.; Dey, Avishek; Krishnamurthy, Satheesh; Matsumi, Noriyoshi and Darr, Jawwad A. (2019). Continuous Hydrothermal Synthesis of Metal Germanates (M₂GeO₄ ; M = Co, Mn, Zn) for High Capacity Negative Electrodes in Li‐ion Batteries. Energy Technology, 8(1), article no. 1900692.

DOI: https://doi.org/10.1002/ente.201900692

Abstract

Nanosized metal germanates (M₂GeO₄; M = Co, Mn, Zn) were synthesised using a continuous hydrothermal flow synthesis process for the first time. Phase‐pure rhombohedral Zn₂GeO₄ nanorods, cubic spinel Co₂GeO₄ nanoparticles, and orthorhombic Mn2GeO4 nanotubes/nanoparticles were obtained. The electrochemical properties of all samples as active materials for negative electrodes in Li‐ion half cells was explored. The galvanostatic and potentiodynamic testing was conducted in the potential range 3.00 to 0.05 V vs. Li/Li⁺. The results suggest that both alloying and conversion reactions associated with Ge contributed to the stored charge capacity; Zn₂GeO₄ showed a high specific capacity of 600 mAh g^-1 (10 cycles at 0.1 A g ^-1) due to alloying and conversion reactions for both Ge and Zn. Mn₂GeO₄ was studied for the first time as a potential negative electrode material in a Li‐ion half‐cell; an excellent specific charge capacity of 510 mAh g^-1 (10 cycles / 0.1 A g^-1) was obtained with a significant contribution to charge arising from the conversion reaction of Mn to MnO upon delithiation. In contrast, Co₂GeO₄ only showed a specific capacity of 240 mAh g^-1, after 10 cycles at the same current rate, which suggested that cobalt had little or no benefit for enhancing stored charge in the germanate.

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