In-situ preparation of mesoporous carbon contained graphite-zinc quantum dots for enhancing the electrochemical performance of LiFePO4

摘要

Conductive porous carbons generally are used as the additives to contact with active materials to generate conductive network for electrodes of commercial lithium ion batteries (LIBs). As a cathode material, LiFePO4 (LFP) has been widely used for LIBs. However, it needs higher quantity of conductive carbons to enhance its electrochemical performances due to the low ion diffusion coefficient and low electronic conductivity. In this work, we synthesize the mesoporous carbon contained graphite-zinc quantum dots (MC-GZQDs) via the carbonization of zeolitic imidazolate frameworks-8 (ZIF-8) under anaerobic condition. X-ray diffraction (XRD) test proves that the MC-GZQDs sample is a kind of graphite-type carbon. The N-2 adsorption and desorption analysis reveals the hierarchical pore structure and typical ordered mesoporous characteristic. High-resolution transmission electron microscopy (HRTEM) indicates that the sample possesses QDs and it has heterogeneous core (metal Zn)-shell (graphite) structure. As an additive, MC-GZQDs can improve both electronic conductivity and ion diffusion coefficient of LFP due to its high conductivity and porous structure. LFP mixing with MC-GZQDs delivers a high rate performance of 154.6mAhg(-1) at a current rate of 0.5C and a capacity retention ratio of approximate 99.9% after 60cycles at 10.0C.