ZIF 67 derived Co-Sn composites with N-doped nano-porous carbon as anode material for Li-ion Batteries /

Abstract

Lithium-ion batteries have acquired much consideration for a long time as an effective and commercial energy storage device. The emerging industry of electric vehicles (EVs) and hybrid electric vehicles (HEVs) demand efficient, stable and high energy densities batteries. Tin (Sn) is the promising element and has attracted great attention due to high theoretical specific capacity (994 mAh g-1) and low cost. The tin (Sn) has some draw backs of volume changing issue during the lithiation and de-lithiation process as anode side material for lithium-ion batteries. To overcome the structure instabilities and increase the overall rate capability of tin based anode material the three composites of CoSn alloy embed in the highly porous nano carbon structure with different amount of carbon and nitrogen were synthesized using 2-methylimidazole as a precursor that led to the formation of SnO2@ZIF-67 framework. Then after carbonization the different composition of CoSn-NC were obtained. The in grown framework of bonding consist of Sn-C and Co-Sn alloy network. The XRD, SEM, FTIR and BET Characterization technique were used to analyze the stable morphology and good structure stability. The electro chemical study of the CoSn-NC composites consists of three molar ratios of 2-methylimidazole were evaluated by the galvanometric charge and discharge cycle and by cyclic voltammetry (CV). The sample CoSn-NC-3 shows the highest reversible capacity of 600 mAh g-1 after 50 cycles at discharge rate of 0.10 A g-1 with 98% coulombic efficiency as compared to the other two sample. The high reversible capacity is to the high amount of N-doped organic linker that led to the higher carbon and nitrogen content that increase the surface area and porosity of the sample. The stable porous carbon structure provide cushion for the volume change of the cobalt tin alloy that increase the stability after high number of cycles.