Self-Optimizing Effect in Lithium Storage of GeO₂ Induced by Heterointerface Regulation

Herein, a heterostructural hexagonal@tetragonal GeO₂ (HT-GeO₂ ) composite has been designed based on density functional theory (DFT) calculations and synthesized via an acidic-heating route dealt with rapid cooling, where the inner hexagonal GeO₂ (H-GeO₂ ) phase is covered by a porous layer of tetragonal GeO₂ (T-GeO₂ ) owing to HF etching. Interestingly, the HT-GeO₂ electrode has a self-optimizing effect in lithium storage induced by heterointerface regulation, where the porous T-GeO₂ layer on the surface of HT-GeO₂ can act as not only a Li⁺ /electron conducting layer, but also a buffer layer, while the inner H-GeO₂ phase can react preferentially with Li ions owing to lower intercalation energy, which is confirmed by operando XRD measurement contributing to thorough lithiation for HT-GeO₂ . Moreover, the heterointerface can enhance the pseudocapacitance effect, which can boost the Li storage and accelerate the discharge-charge process. As a result, a large capacity of 984 mAh g^-1 after 500 cycles at 2 A g^-1 and a capacity of 430 mAh g^-1 at a high current density of 20 A g^-1 are delivered. This work provides an easy and efficient way to improve the cycling stability of the GeO₂ anode, and the T-GeO₂ phase would be a novel anode material in energy storage devices.