Correlations of Precursor and Carbon Coating with Electrochemical Property of 2D Graphitic Carbon Nitride (g-C<sub>3</sub>N<sub>4</sub>) Nanosheets as High-Reversibility Cathode of Nonaqueous Al-Ion Batteries
Jiahui Li, Dongwei Ma, Gui Lu, Dong Fu, Carlos Ponce de León, Jia Hong Pan
Abstract
Al-ion batteries (AIBs) represent promising multivalent-ion battery alternatives to Li-ion batteries (LIBs). Exploration of cathode materials is the key to improving the electrochemical performance of AIBs. Here we demonstrate a promising AIB cathode candidate based on two-dimensional graphitic carbon nitride (g-C 3 N 4 ) nanosheets with reversible de/embedding of [AlCl 4 ] − anions in its special layered porous structure during the cyclic charge/discharge process. To address the sluggish ion/charge transportation kinetics that is inherently present in AIBs due to the intrinsically low conductivity of g-C 3 N 4, we optimize different synthetic precursors of g-C 3 N 4 including dicyandiamide, urea, and melamine and, further, develop a facile method for uniformly coating a N-doped carbon (N–C) coating layer on the optimal g-C 3 N 4 derived from dicyandiamide. The resultant AIBs consisting of the g-C 3 N 4 @N–C cathode and Al metal anode in the AlCl 3 /[EMIm]Cl electrolyte exhibit an initial capacity of ∼54.9 mAh·g –1 at 0.2 C with a high Coulomb efficiency ∼99.9%, and they possess long-term cycling over 200 cycles. The underlying charge/discharge process of AIBs, revealed by the ex situ X-ray diffraction and scanning electron microscopy analyses, involves the extraction/insertion of Al species (mainly Al 3+, AlCl 4 –, and Al 2 Cl 7 – ) into the g-C 3 N 4 crystal lattices with the formation of intermediate Al 8 C 3 N 4 and (ClCN) 3 .