Cellulose-grafting boosted pyrolysis nucleation: Achieving low-temperature construction of hard carbon anodes with long low-voltage plateau and ultrafast Na storage kinetics

Abstract

Biomass-derived hard carbon (BHC) with low-voltage plateau (LP) is a promising anode material for sodium ion batteries. However, ultrahigh carbonization temperatures to obtain LP and slow electrochemical reaction kinetics in LP make it difficult to achieve low cost and high rate performance. Herein, a cellulose grafting reaction is proposed to modulate the pyrolysis nucleation process of biomass, which makes it possible to obtain a BHC with graphitic nanodomain structure at 800 °C, similar to the hard carbon prepared at the traditional 1300 °C. Moreover, the nitrogen doping introduced by the grafting reaction is highly preserved at low carbonization temperatures, which induces a dramatic shift in the electrochemical reaction kinetics and converts the typical slow diffusion control process in LP to an ultrafast pseudocapacitive control process. As a result, the prepared N-doped BHC simultaneously realizes long pseudocapacitive-control LP, high reversible capacity, excellent rate capability, and ultralong cycle life in sodium ion half/full cell. More significantly, the structure formation mechanism, Na-storage mechanism, and the root causes of electrochemical reaction kinetic shifts in the LP of such a N-doped BHC are studied in detail, which provides a constructive view for the low-temperature construction of BHCs with long LP and high rate performance.