Fabrication,Structure And Electrochemical Properties Of Fe_xO_y/C Composite Anode Materials For Iithium Ion Batteries

Among transition metal oxide anode materials, iron oxides are considered to be promising anode materials for LIBs because of their advantages of high theoretical capacities, environmental benignity, high abundance, low cost, etc. However, their practical application in anode materials is still hindered by their poor cycling performance arising from the severe aggregation and huge volume change during lithium insertion/extraction process. In the present study, commercial nano-sized Fe2O3and acetylene black are used as starting materials to fabricate FexOy/C composites with different types of FexOy of Fe2O3, Fe3O4as anode materials for lithium ion batteries. AB is introduced into Fe2O3particles by ball-milling and followed by carbothermal reduction to form FexOy/C composites. The effects of the addition of acetylene black, the temperature of carbothermal reduction on the structure and electrochemical properties of the FexOy/C composites are investigated by XRD, SEM, TEM, etc. and electrochemical testing of galvanostatic charge-discharge, cyclic voltammograms, etc. The key factors that affect the cycle stability of the composites and its mechanism are also discussed.The results show that ball milling with acetylene black can effectively disperse the nano-Fe2O3particles, hence improving both the electrochemical capacity and cycle stability of the composites. The capacities of Fe2O3/AB composites decrease and the cycle stability increase with the increasing contents of acetylene black. The initial discharge capacities of the Fe2O3/AB composites decrease from827to654mAh/g with the AB additions increasing from30to70wt.%, and the capacity retention increases from29%to81%after100cycles. The Fe2O3/C composites with60wt.%AB addition shows the highest capacity of397mAh/g among the composites after100cycles.There is no phase transformation in Fe2O3at calcination temperature of300℃under N2atmosphere. Partial Fe2O3starts to convert to Fe3O4at400℃, forming Fe3O4/Fe2O3/C composite. Fe2O3is fully converted to Fe3O4at the temperature range of500-700℃. The FexOy/C composites obtained by calculation at different temperatures all show superior overall electrochemical properties than their original Fe2O3/AB mixtures.For the composites of Fe3O4/C, the nano-Fe304particles are well dispersed in the AB matrix. The connecting of the Fe3O4and the AB particles is enhanced after the carbothermal reduction. The composites obtained from Fe2O3/AB mixtures with60and70wt.%AB additions and carbothermal reduced at600℃possess capacity of ca.450mAh/g after100cycles, showing retentions of85%and95%, respectively. The favorable electrochemical performance of the Fe3O4/C composites is attributed to the homogeneous distribution of the Fe3O4nanoparticles in the carbon matrix, which buffers effectively the volume change and prevents the agglomeration of the metallic iron during cycling, enhances the connecting of the Fe3O4and the AB particles as well as the superior electronic conductivity of Fe3O4, which improves the electronic contact of the active material.