A covalent heterostructure of monodisperse Ni 2P immobilized on N, P-co-doped carbon nanosheets for high performance sodium/lithium storage

摘要

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 (Ni2P@NPC), which exhibits a remarkable reversible discharge capacity and outstanding long-term durability for both sodium storage (361?mA?h?g-1@100?mA?g-1after 300 cycles, and 181?mA?h?g?1@500?mA?g-1after 1200 cycles) and lithium storage (1555?mA?h?g-1@100?mA?g-1after 130 cycles, and 603?mA?h?g-1@1000?mA?g-1after 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.