Electrochemical performance and structure evolution of core-shell nano-ring α-Fe2O3@Carbon anodes for lithium-ion batteries

Core-shell nano-ring alpha-Fe2O3@Carbon (CSNR) composites with different carbon content (CSNR-5%C and CSNR-13%C) are synthesized using a hydrothermal method by controlling different amounts of glucose and alpha-Fe2O3 nano-rings with further annealing. The CSNR electrodes exhibit much improved specific capacity, cycling stability and rate capability compared with that of bare nano-ring alpha-Fe2O3 (BNR), which is attributed to the core-shell nano-ring structure of CSNR. The carbon shell in the inner and outer surface of CSNR composite can increase electron conductivity of the electrode and inhibit the volume change of alpha-Fe2O3 during discharge/charge processes, and the nano-ring structure of CSNR can buffer the volume change too. The CSNR-5%C electrode shows super high initial discharge/charge capacities of 1570/1220 mAh g(-1) and retains 920/897 mAh g(-1) after 200 cycles at 500mA g(-1) (0.5C). Even at 2000 mAg(-1) (2C), the electrode delivers the initial capacities of 1400/900 mAh g(-1), and still maintains 630/610 mAh g(-1) after 200 cycles. The core-shell nano-rings opened during cycling and rebuilt a new flower-like structure consisting of alpha-Fe2O3@Carbon nano-sheets. The space among the nano-sheet networks can further buffer the volume expansion of alpha-Fe2O3 and facilitate the transportation of electrons and Li+ ions during the charge/discharge processes, which increases the capacity and rate capability of the electrode. It is the first time that the evolution of core-shell alpha-Fe2O3@Carbon changing to flower-like networks during lithiation/de-lithiation has been reported. (C) 2016 Elsevier B.V. All rights reserved.