Synthesis Of Graphene Wrapped Selenium-based Compounds Nanocomposites For Lithium-ion Batteries

This paper mainly devotes to synthesizing nanocomposites with graphene for higher specific capacity and more stable cycle performance for lithium ion batteries (LIBs). Firstly, a green, novel, simple, and low cost method is developed to prepare graphene-based nanocomposite for achieving high-performance electrode materials of LIBs. Secondly, a graphene-based nanocomposite with reduced graphene oxide (RGO) wrapped SeS2@PANI core-shell structure is prepared to be applied in LIBs. The main contents of this paper are as following.1. We present a novel strategy to synthesize graphene oxide-wrapped nanocrystals composite (GO@NCs). In the process, chitosan (CS). which is biocompatible, cheap, low toxic and environmental friendly, is elected as an assistant to facilitate the formation of the GO@NCs. This method is mainly based on hydrogen bonding between groups of amino and hydroxyl in CS chains and oxygen-containing functional groups on GO sheets, and electrostatic interaction between positively charged CS chains and negatively charged GO sheets. The whole assembly process can be accomplished at room temperature within two minutes. And it can be widely applied in preparing various kinds of GO-wrapped nanocrystals composites, and the coated GO can further enhance the electrochemical performance of the GO@NCs composite. So we prepared GO@SnSe nanorods, GO@Fe2O3 nanorices Fe2O3, GO@CoSn(OH)6 nanocubes, GO@ selenium (Se) nanospheres by this method. And the prepared GO-wrapped tin selenide nanorods composite (GO@SnSe) is evaluated as an anode for lithium ion batteries and delivers an enhanced reversible capacity of 764 mA h g-1 at the current density of 100 mA g-1 after 100 cycles, which is much higher than that of bare SnSe nanorods.2. We firstly prepared SeS2 nanocubes in aqueous solution at room temperature. And then the pre-prepared sample is coated with a layer of polyaniline (PANI) to form the core-shell structure (SeS2@PANI) by the in situ chemical oxidative-polymerization effect of aniline at low temperature. Finally GO sheets is wrapped outside to form double protection layer through electrostatic interactions between GO and PANI, which can be denoted as SeS2@PANI/RGO after HI solution is added to reduce GO. This nanocomposite exhibits more stable cycling performance and batter rate performance compared to that of bare SeS2 nanocubes. After 100 charge/discharge cycles, the SeS2@PANI/RGO electrode shows a specific discharge capacity of nearly 600 mA h g-1 within the voltage range of 1.7-2.8 V (vs. Li/Li+) at a current density of 100 mA g-1. For the rate performance, the SeS2@PANI/RGO electrode exhibits a discharge capacity of 500 mA h g-1 at a large current density of 1000 mA g-’. And after the current density is reduced to 100 mA g-1, the specific capacity also increases to 600 mA h g-1. Besides in the whole cycling process, the nanocomposite electrode shows high coulombic efficiency nearly 100%.