Gongkai Wang

Three-Dimensionally Hierarchical Graphene Based Aerogel Encapsulated Sulfur as Cathode for Lithium/Sulfur Batteries

A simple and effective method was developed to obtain the electrode for lithium/sulfur (Li/S) batteries with high specific capacity and cycling durability via adopting an interconnected sulfur/activated carbon/graphene (reduced graphene oxide) aerogel (S/AC/GA) cathode architecture. The AC/GA composite with a well-defined interconnected conductive network was prepared by a reduction-induced self-assembly process, which allows for obtaining compact and porous structures. During this process, reduced graphene oxide (RGO) was formed, and due to the presence of oxygen-containing functional groups on its surface, it not only improves the electronic conductivity of the cathode but also effectively inhibits the polysulfides dissolution and shuttle. The introduced activated carbon allowed for lateral and vertical connection between individual graphene sheets, completing the formation of a stable three-dimensionally (3D) interconnected graphene framework. Moreover, a high specific surface area and 3D interconnected porous structure efficiently hosts a higher amount of active sulfur material, about 65 wt %. The designed S/AC/GA composite electrodes deliver an initial capacity of 1159 mAh g−1 at 0.1 C and can retain a capacity of 765 mAh g−1 after 100 cycles in potential range from 1 V to 3 V.

Effect of VO 4 3– Substitution on the Electrochemical Properties of a LiSn 2 (PO 4 ) 3 Anode Material

LiSn2(PO4)3 anion was used to partially substitute for VO43– in the Nasicon compound of LiSn2(PO4)3via a sol-gel method. XRD analysis revealed that the LiSn2(PO4)3-substituted samples did not have a single LiSn2(PO4)3 phase, and some secondary phases like SnO2 and SnP2O7 appeared. Introduction of the LiSn2(PO4)3 anion did not prevent the LiSn2(PO4)3 compound from decomposing during the initial lithiation; however the LiSn2(PO4)3 anion substitution remarkably enhanced the rate capability and cycling performance of the products because they reduced the charge transfer impedance, increased the lithium ion diffusion, and strengthened the role of the Li3VO4 matrix due to the precipitation of the Li3VO4 phase. Of the substituted samples, the sample with a nominal composition of LiSn2(PO4)2.5(VO4)0.5 delivered a capacity of 449.2 mA·h/g at a rate of 0.25 C after 25 cycles and 373.8 mA·h/g at 2 C rate. Those values surpassed some previous reports on LiSn2(PO4)3 and the LiSn2(PO4)3/C composites. Accordingly, the partial substitution of phosphorus by vanadium in LiSn2(PO4)3 is a feasible technique to remarkably improve its electrochemical properties.