Synthesis And Electrochemical Performance Of Si-based Lithium-ion Batteries Anode Materials

Silicon(Si)has emerged as one of the most promising high energy density lithium anode material to the traditional graphite electrodes,due to its high specific capacity is 10 times higher than that of traditional graphite anode.However,serious capacity fading caused inevitably by more than 300%volume change and pulverization during charge-discharge has become the most critical adverse factors affecting its applications.In this paper,different silicon sources and carbon sources are used to prepare a variety of different morphologies and structures of silicon-based lithium ion battery anode materials,which can improve electrochemical performance and reduce the pulverization of materials from the volume effect:The novel folded-hand Si/C 3D networks have been constructed by chemical vapor deposition coupled with ultrasonic atomization and employed successfully for binder-free anode in LIBs.The transition carbon layer provides a stable,firm and tough adhesion point for the deposition of silicon,and improves the conductivity of the electrode.Moreover,the transition carbon layer is important for the formation of 3D networks morphology.The spiciform Si/C bunches will be formed without the transition carbon layer.They reveal an excellent reversible capacity of 2277 mAh/g at 1C,and retaining a reversible capacity of 2167 mAh/g after 100 cycles.The LiFePO4//Si/C full cell can maintain high capacity of 137 mAh/g and capacity retention of 92%after 500 cycles at 1 C rate.The construction for the folded-hand Si/C 3D networks is an effective and feasible design for binder-free Si-based anode and is also a new concept for next generation lithium-ion batteries.The yolk-shell structured multilayer silicon/carbon composites microspheres were synthesized by heterogeneous continuous nucleation method,hydrothermal and magnesium thermal reduction method.The yolk-shell structured multilayer silicon/carbon composites microspheres have both controllable shell thickness and the number of layers,and employed for silicon-based anode material.The silicon layers and carbon layers of the multilayer silicon/carbon composites microspheres are controllable,and the thickness of the silicon and carbon layers can be adjusted by controlling the amount of raw materials.The initial charge capacities of single-,double-,triple-layer silicon/carbon microspheres reach 1797,2455 and 2065 mAh/g at 0.1C,and shows capacities of 631,1018,444 mAh/g when increased the rate at 5C.The discharge capacity of double-layer silicon/carbon microspheres suggests that a capacity retention of 88.7%at 0.1C.The double-layer silicon/carbon microspheres shows best performance is mainly ascribed to the reasonable structure with the thin shell to shorten the lithium diffusion distance,provide more active sites and numerous pores to facilitate the electrolyte permeation.In order to obtain a better pore structure and further improve the electrochemical performance,the carbon layer in the hydrothermally synthesized single-layer silicon/carbon microspheres is partially etched to obtain the cage-like Si/C microspheres.The cage-like carbon layer can absorb the volume expansion of silicon during charge/discharge,and maintain the integrity of the material.The results show that the cage-like Si/C microspheres obtained by etching a part of carbon with potassium permanganate have larger specific surface area and better pore structure than the original single-layer silicon/carbon microspheres,and shows better electrochemical performance.The initial charge capacity of the cage-like Si/C microspheres is 1926 mAh/g at 0.1C,and maintaining capacity of 1790 mAh/g with coulombic efficiency of 99%after 200 cycles.Reversible capacity of the cage-like Si/C microspheres is keep 963 mAh/g when increased the rate at 5C.