Highly-dispersed Ge quantum dots in carbon frameworks for ultra-long-life sodium ion batteries

Abstract

Metal germanium (Ge) with a high theoretical capacity of 590 mA h g⁻¹ is regarded as a promising anode material for sodium ion batteries, but it suffers from a fast capacity decay problem due to the serious agglomeration of Ge particles caused by the drastic volume change during the sodiation/desodiation process. Constructing highly dispersed ultrafine Ge nanoparticles is a possible way to address this problem. However, reported methods to obtain highly dispersed metal nanoparticles encountered problems of poor electrochemical activity or non-uniform particle size. In this work, we proposed a new in situ confined polymerization method for preparing highly dispersed Ge quantum dots (QDs). Due to the high dispersion of Ge QDs in carbon frameworks derived from poly(ionic liquid) networks, the obtained Ge@C nanocomposite could effectively avoid the agglomeration of Ge particles. When applied as the anode material for sodium ion batteries, the Ge@C nanocomposite shows ultra-long cycle life and high rate capability. At a current density of 1500 mA g⁻¹, the Ge@C electrode could display a high capacity of 201 mA h g⁻¹ after 5000 cycles. This method could be extended to prepare other highly dispersed metal nanoparticles and achieve fairly efficient electrode materials for new-type secondary batteries.