Exploring the Spinel Phase of Zn ₂ GeO ₄ as an Anode for Li-Ion Storage

The recent discovery of an effective method for synthesizing the spinel phase of zinc germanate ( c -Zn 2 GeO 4 ) gives an interesting opportunity to study its properties and potential applications. Then, this work combines experimental and theoretical approaches to understand its electrochemical behavior in depth as a Li-ion host anode. Its electrochemical evaluation shows that the c -Zn 2 GeO 4 -based electrode delivers a stable capacity of 226 mAh g –1 at 0.1 C with an efficiency of 98% after 100 cycles with kinetics controlled by insertion and capacitive contributions at low and high scan rates, respectively. On the other hand, DFT calculations corroborate that Zn 2 GeO 4 can crystallize under a spinel structure, where a single Li-atom diffusion occurs preferentially along its [1̅00] direction, displaying a minimum energy barrier of 2.01 eV. During the lithiation reaction, DFT calculations reveal that Li n Zn 2 GeO 4 structures are thermodynamically stable with a minimum formation energy of −1.21 eV and a maximum volume expansion of 195%. The open-circuit voltage graphs suggest that 1 mol of c -Zn 2 GeO 4 could store 12 mol of Li, delivering a maximum theoretical capacity of 1203 mAh g –1 . Moreover, AIMD simulations of Li n Zn 2 GeO 4 structures expose the rupture of Zn–O and Ge–O bonds and the formation of Li–O, Li–Ge, and Li–Zn bonds upon lithiation.