Ni3S2/NiSe2 hollow spheres with low bonding energy Ni-Se bonds for excellent lithium-ion charge-discharge stability

Abstract

The capacity and cycle stability of anode materials determine their application prospects in lithium-ion batteries (LIBs). Ni3S2 has attached much attention due to its high theoretical capacity as anode materials for LIBs. However, the inherent low conductivity and inevitable volume expansion during the charge-discharge process of Ni3S2 seriously limit its practical application. Compared with Ni3S2, NiSe2 owns higher Li+ conductivity for the lower binding energy of Ni-Se caused by the larger radius of Se. Herein, Ni3S2/NiSe2 hollow spheres have been prepared through an in situ gas phase selenization method, in which the sulfur atoms in Ni3S2 are partially replaced by Se atoms. When served as anode materials for LIBs, Ni3S2/NiSe2 exhibits an initial capacity of 1054.8 mA h g−1 at 100 mA g−1 and reversible capacity of 709 mA h g−1 at the current density of 100 mA g−1 after 200 cycles. Compared with Ni3S2 and NiSe2, the superior electrochemical performance of Ni3S2/NiSe2 can be attributed to the synergistic effect of two crystalline phases Ni3S2 and NiSe2 in Ni3S2/NiSe2, as well as the weaker electronegativity of Ni-Se benefiting to improve the reaction kinetics in the process of Li+ charge-discharge. Moreover, the pseudocapacitance behavior of Ni3S2/NiSe2 in the lithium storage process is also verified by electrode dynamic analysis. Our work provides a new strategy for the design of efficient lithium storage materials by constructing weak metal-chalcogen bonds to improve material conductivity and reduce energy consumption during conversion reactions.