Boosting reversible lithium storage in two-dimensional C3N4 by achieving suitable adsorption energy via Si doping

ABSTRACT Graphitic carbon nitride (C3N4) is the most widely reported member of the carbon nitride family because of its large pores which serve as alkali-metal atom storage sites. However, adsorption of Li atoms into these triangular pore sites occur at a high adsorption energy (Ead) of ∼4.2 eV which surpasses the desorption energy of bulk Li (3 eV) thereby resulting in ineffective desorption. Lithium storage in C3N4 occurs via an intercalation/deintercalation process therefore the inability of adsorbed Li atoms to desorb from its structure results in structural instability, poor conductivity and limited reversible capacity. Here, we show that by doping Si atoms into the pore sites of C3N4, the Li Ead can be significantly decreased to 2.51 eV. This suitable Ead enabled effective Li transport, improved charge transfer, modulated the electronic conductivity, decreased the Li diffusion barrier and boosted the lithium storage capacity to 557.7 mAh/g. These results show that Si doping is an effective way to resolve the problems associated with C3N4 and to achieve superior electronic properties and lithium storage capacity. These interesting results show the potential of Si doped C3N4 for lithium ion batteries and this approach can be extended to other carbon nitride structures.