Construction of phosphorus-doping with spontaneously developed selenium vacancies: Inducing superior ion-diffusion kinetics in hollow Cu2Se@C nanospheres for efficient sodium storage

Achieving high-efficiency sodium storage in metal selenides is still severely constrained in consideration of their inferior electronic conductivity and inadequate Na' insertion pathways and active sites. Heteroatom doping accompanied by spontaneously developed lattice defects can effectively tune electronic structure of metal selenides, which give a strong effect to motivate fast charge transfer and Na' accessibility. Herein, we finely designed and successfully constructed a fascinating phosphorus-doped Cu2Se@C hollow nanosphere with abundant vacancy defects (Cu2PxSe1-x@C) through a combination strategy of selenization of Cu2O nanosphere template, self-polymerization of dopamine, and subsequent phosphorization treatment. Such exquisite composite possesses enriched active sites, superior conductivity, and sufficient Na' insertion channel, which enable much faster Na' diffusion rates and more remarkable pseudocapacitive features. Satisfyingly, the Cu2PxSe1-x@C composites manifest the supernormal sodium-storage capabilities, that is, a reversible capacity of 403.7 mA h g-1 at 1.0 A g-1 over 100 cycles, and an ultrastable cyclic lifespan over 1000 cycles at 20.0 A g-1 with a high capacity-retention of about 249.7 mA h g-1. The phase transformation of the Cu2PxSe1-x@C involving the intercalation of Na' into Cu2Se and the following conversion of NaCuSe to Cu and Na2Se were further demonstrated through a series of ex-situ characterization methods. DFT results demonstrate that the coexistence of phosphorusdoping and vacancy defects within Cu2Se results in the reduction of Na' adsorption energy from -1.47 to -1.56 eV improving the conductivity of Cu2Se to further accelerate fast Na' mobility. (c) 2022 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by ELSEVIER B.V. and Science Press. All rights reserved.