Self-supporting ZnP2@N, P co-doped carbon nanofibers as high-performance anode material for lithium-ion batteries

Abstract

Searching for high specific capacity anode materials with an optimized structure to achieve high energy density, long cycling life-span, and high rate performance for lithium-ion batteries (LIBs) is a pressing assignment. Metal phosphides have aroused much attention, however, enormous volume variations, poor electrical conductivity, and aggregation of nanoparticles hamper their practical applications. Herein, ZnP2 nanoparticles grown on N, P co-doped carbon nanofibers (ZnP2 @NPCNFs) composite synthesized by electrospinning and heat treatment is reported to directly act as binder-free anode in LIBs. The 3D self-standing ZnP2 @NPCNFs featuring good flexibility can not only boost conductivity and alleviate the volumetric fluctuations in the cycling course, but also buffer the agglomeration and pulverization of nanoparticles. Lithium storage of ZnP2 @NPCNFs electrode obey the conversion reaction mechanism. Besides, the additional lithium intercalation active sites created by the doped-nitrogen and the existence of PC bond along with the space-confined effect of NPCNFs are conjointly beneficial to endow the ZnP2 @NPCNFs electrode with distinctive electrochemical properties. When assembled as the anode, the ZnP2 @NPCNFs electrode reached a high reversible capacity of 746 mA h g−1 after 100 cycles at 0.2 A g−1 and 406.49 mA h g−1 after 1000 cycles at 2 A g−1. Electrochemical tests manifest that most of the capacity contribution comes from capacitive process. Moreover, the similar superior electrochemical performances are obtained in the LiFePO4//ZnP2 @NPCNFs full cell. Generally, this study widens researchers’ horizons to conceive rational structure of metal phosphides anodes in LIBs with high capacity conservation.