Amorphous mesoporous GeO x anode for Na-ion batteries with high capacity and long lifespan.

It is recently demonstrated that amorphous Ge anode shows higher reversible Na-ion storage capacity (590 mA h g-1 ) than crystallized Ge anode (369 mA h g-1 ). Here, amorphous GeO x anode is prepared by a simple wet-chemistry reduction route at room temperature. The obtained amorphous GeO x shows a porous hierarchical architecture, accompanied with a Brunauer-Emmett-Teller surface area of 159 m2  g-1 and an average pore diameter of 14 nm. This unique structure enables the GeO x anode to enhance the Na-ion/electron diffusion rate, and buffer the volume change. As anode for Na-ion battery, high reversible capacity over 400 mA h g-1 , fine rate capability with a capacity of 200 mA h g-1 maintained at 3.0 A g-1 and long-term cycling stability with 270 mA h g-1 even over 1000 cycles at 1.0 A g-1 are obtained.