Enabling superior rate capability and reliable sodium ion batteries by employing galvanostatic-potentiostatic operation mode

Abstract Hard carbon (HC) is one of the widely used anodes for Sodium-ion batteries (SIBs) thanks to their extensive resources and excellent stability. However, the commercial HC is still confronted with inferior rate capability and serious sodium precipitation after assembling the full battery with cathode. Herein, an efficient and feasible galvanostatic-potentiostatic operation mode is introduced to solve above issues. The sodium storage mechanism has been clarified by a series of advanced characterization techniques. The results indicate that Na-ions firstly adsorb on the oxygen functional group (C O) at high voltage region and then adsorption and filling of sodium co-exist at low voltage region in galvanostatic step. Finally filling of sodium in micropores occurs in potentiostatic step. The results demonstrate that potentiostatic step can enable more Na-ions filling in the pores with reduced electrochemical polarization and can reduce the risk of sodium precipitation as well. As a result, a high capacity of ~300 mAh g−1 at the current range of 0.1 C–5 C can be achieved for a HC-based half-cell, and at a capacity retention of 5 C from 58% to 73% (relative to 1 C) has been observed for pouch cell after introducing potentiostatic step, confirming the feasibility of proposed operation mode.