A One-pot Self-assembly Strategy Of Synthesizing High-performance Transition Metal Oxides@Carbon Micro/nanocomposites For Lithium-ion Storage

Rechargeable lithium-ion batteries(LIBs)have been extensively utilized as power sources,while the power and energy density remain insufficient to satisfy the requirements of the fast developing electronic devices.To improve the overall capacity of LIBs,the development of high capacity anode and cathode materials is critically necessary.Since the specific capacity of current cathodes is limited to about 200 mAh g-1,the overall battery capacity could be increased if the commercial graphite anode(372 mAh g-1)is replaced by the novel anodes with higher specific capacity.To date,transition metal oxides(TMOx)with high rechargeable capacities following the conversion mechanism are considered as promising alternatives.MOx as anode materials were first proposed by Poizot et al.in 2000.Among all the TMOx,MnOx and FeOx have become the most promising alternatives due to their high specific capacity,low cost and various nanostructures.However,since the low electrical conductivity and large volume change during lithiation and delithiation,the rate and cyclic performance is not so satisfactory,hindering the development of these materials.Herein,to address these concerns,an in-situ self-assembled synthetic strategy of carbon-coated TMOx micro/nanocubes was developed to achieve mesoporous micro/nanostructure with homogeneously inter-dispersed carbon networks by a one-pot method.Accordingly,by tuning the hydrothermal temperature and annealing temperature,as-obtained TMOx@C with different average sizes were successfully prepared.The resultant TMOx@C,taking both of the advantages of mesoporous nanostructure and carbon hybridization,exhibited significantly enhanced cycling stability and rate performance as anode for lithium ion batteries.The detailed research contents are listed as follows:Firstly,the Mn3O4@C micro/nanocubes was prepared by hydrothermal method,using glucose as reductant and carbon source.By changing the ratio of raw materials,hydrothermal temperature,time,and annealing temperature,suitable carbon content and morphology of the Mn3O4@C micro/nanocubes were obtained.The method greatly simplifies the carbon-coated preparation process.Through a series of contral experiments,The as fabricated Mn3O4@C nanocubes exhibit large reversible specific capacity(879 mAh g-1 at the current density of 100 mA g-1)as well as outstanding cycling stability(86%capacity retention after 500 cycles)and rate capability,making them promising as anodes in lithium ion batteries.Secondly,Fe2O3@C hollow nanospheres were also fabricated successfully with glucose as a reducing agent and carbon source.By changing the raw material ratio,hydrothermal temperature,time,and annealing temperature,optimized Fe2O3@C hollow nanospheres were obtained.The sample provide a reversible capacity of 998 mAh g-1 at a current density of 100 mA g-1.At a large current density of 2 A g-1,it still delivers a reversible capacity of 580 mAh g-1.After being charge/discharged at 1 A g-1 for 700 cycles,a capacity retention of 85%can be achieved.Above all,our research has demonstrated the universality of this strategy,providing a potentially effective solution for the large-scale fabrication and application of TMOx-based energy storage mateirals.