Cascading Boost Effect on the Capacity of Nitrogen-Doped Graphene Sheets for Li- and Na-Ion Batteries

Specific capacity and cyclic performance are critically important for the electrode materials of rechargeable batteries. Herein, a capacity boost effect of Li- and Na-ion batteries was presented and clarified by nitrogen-doped graphene sheets. The reversible capacities progressively increased from 637.4 to 1050.4 mAh g^-1 (164.8% increase) in Li-ion cell tests from 20 to 185 cycles, and from 187.3 to 247.5 mAh g^-1 (132.1% increase) in Na-ion cell tests from 50 to 500 cycles. The mechanism of the capacity boost is proposed as an electrochemical induced cascading evolution of graphitic N to pyridinic and/or pyrrolic N, during which only these graphitic N adjacent pyridinic or pyrrolic structures can be taken precedence. The original and new generated pyridinic and pyrrolic N have strengthened binding energies to Li/Na atoms, thus increased the Li/Na coverage and delivered a progressive capacity boost with cycles until the entire favorable graphitic N transform into pyridinic and pyrrolic N.