A covalent heterostructure of monodisperse Ni2P immobilized on N, P-co-doped carbon nanosheets for high performance sodium/lithium storage

The high volume expansion and serious agglomeration during sodiation/lithiation of transition metal phosphides (TMPs) raise up challenging kinetic issues and rapid capacity fading upon cycling. The good dispersion and confined movement of individual TMP particles are critical in mitigating the agglomeration, which however have been rarely concerned. In this work, we report a novel covalent heterostructure with monodisperse Ni2P immobilized on N, P-co-doped carbon nanosheets (Ni2[email protected]), which exhibits a remarkable reversible discharge capacity and outstanding long-term durability for both sodium storage (361 mA h g-1@100 mA g-1 after 300 cycles, and 181 mA h g−1@500 mA g-1 after 1200 cycles) and lithium storage (1555 mA h g-1@100 mA g-1 after 130 cycles, and 603 mA h g-1@1000 mA g-1 after 800 cycles). Most importantly, using the in-situ TEM visualized technique, we demonstrate that the immobility and monodisperse nature of Ni2P are responsible for the agglomeration-free charge storage process upon cycling. The density functional theory (DFT) calculations reveal the strong covalent coupling between Ni2P and NPC, which realizes the electronic structure engineering of both TMP and carbon buffer, and uncovers the origin of long-term stability and outstanding capacity.