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.