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-Zn2GeO4) 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-Zn2GeO4-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 Zn2GeO4 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 LinZn2GeO4 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-Zn2GeO4 could store 12 mol of Li, delivering a maximum theoretical capacity of 1203 mAh g–1. Moreover, AIMD simulations of LinZn2GeO4 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.