The amorphous GeOx (x < 1) was synthesized and investigated its suitability as a Na-ion battery anode. GeOx was synthesized by oxidizing Zintl-phase NaGe with isopropyl alcohol at room temperature. The amorphous GeOx showed good electrochemical Na storage as an anode for Na-ion batteries, with first reversible capacity of 342 mAh g (1), high power of 237 mAh g (1) (6 A g (1)), and cycle performance, retaining a capacity of 216 mAh g (1) after 40 cycles. (C) 2016 Elsevier Ltd. All rights reserved.