Structural design of Ge-based anodes with chemical bonding for high-performance Na-ion batteries

Abstract

Ge-based anodes for Na-ion batteries (NIB) usually suffer from sluggish reaction kinetics, low initial Coulombic efficiency, poor reversible capacity, and short cycling life due mainly to its rigid diamond-like structure. Here we report our findings in characterization and application of a GeP anode with a flexible layered structure, synthesized by a simple mechanochemical method. When tested as the anode for NIBs, the GeP undergoes a self-healing Na-storage process that involves intercalation, conversion, and alloying, as co-revealed by ex-situ X-ray diffraction, HRTEM, Raman spectroscopy, and X-ray photoelectron spectroscopy analysis. The peculiar self-healing phenomenon derives from its ultra-low formation energy (−0.19 eV) for reconstruction of the original layered structure, as confirmed by first-principle calculations. The low formation energy also enables the formation of chemical bonding between layered GeP and graphite, thus achieving unprecedented performances among all reported anode materials based on Group IVA- and Group VA elements. The structural design strategy guided by formation energy of desirable phases is also applicable to the development of other energy-storage materials.