Improving the Performance of Hard Carbon//Na3V2O2(PO4)2F Sodium-Ion Full Cells by Utilizing the Adsorption Process of Hard Carbon.

Hard carbon has been regarded as a promising anode material for Na-ion batteries. Here, we show, for the first time, the effects of two Na+ uptake/release routes, i.e., adsorption and intercalation processes, on the electrochemical performance of half and full sodium batteries. Various Na+-storage processes are isolated in full cells by controlling the capacity ratio of anode/cathode and the sodiation state of hard carbon anode. Full cells utilizing adsorption region of hard carbon anode show better cycling stability and high rate capability compared to those utilizing intercalation region of hard carbon anode. On the other hand, the intercalation region promises a high working voltage full cell because of the low Na+ intercalation potential. We believe this work is enlightening for the further practical application of hard carbon anode.