Synthesis And Electrochemical Properties Of High Performance Iron And Manganese Oxides/Sulfides And Carbon Anode Materials

Lithium ion battery has attracted extensive attention because of its advantages of higher energy density,better safety,wider temperature range and environmental friendliness.The electrode material is vital to the electrochemical performance of lithium ion battery.Nowadays,commercial lithium ion battery cathode materials are relatively diverse,but the anode materials are relatively single and the most commonly use for graphite anode materials.But limited by a relatively low theoretical capacity(372 mAh/g),commercial graphite anode has been unable to meet people's demand.Therefore,the research and development of electrode materials with higher theoretical capacity is very important.Among them,nitrogen-doped porous carbon materials have been widely studied due to their advantages of good electronic condunctivity,benign wettability,facile preparation and large specific surface area,and transition metal oxides/sulfides,especially those of iron oxides and manganese oxides/sulfides,due to their advantages of high theoretical capacity,abundant resources and low cost.This paper also starts from these materials,and strives to explore the lithium ion battery anodes with higher performance through the innovation of the synthesis method,morphology and structure.The main researches can be listed as follows:(1)Based on the coordination reaction of 2,2'-dipyridine and KOH activation,the nitrogen-doped porous carbon materials were prepared after heat treatment.Compared with carbon before activation,the specific surface area of the activated carbon has increased nearly 5 times(up to 962 m²/g).Moreover,the doped nitrogen also caused more active sites of the carbon material.As for lithium ion battery anode,it was found that the specific capacity of 603 mAh/g could be maintained at the current density of 0.25 A/g after 400cycles,which was much higher than the 372 mAh/g of commercial graphite anode,showing excellent cyclic stability.Used as the electrode material for supercapacitors,it could maintain a high coulomb efficiency of 94%at the current density of 1 A/g after 6000 cycles,showing a long cycle life.(2)Using glucose and urea as carbon and nitrogen doping,combining with ZnCl₂modified-NaCl template method and subsequently annealing,a wrinkled paper-like nitrogen-doped porous carbon material was constructed.Compared to carbon with a paper-like carbon structure becasue without ZnCl₂addition,this wrinkled structure has a raised nearly doubled the larger specific surface area of 1658.6 m²/g and richer hole structure.At the same time,the higher graphitization degree and the appropriate content of nitrogen doping after activation,lead to the high reversible capacity and excellent cycling performance of porous carbon materials including the specific capacity of 1079 mAh/g can be maintained at 0.35 A/g after 1000 cycles and 693 mAh/g at 1 A/g after 400 cycles.(3)The composite of Fe₃O₄coated with nitrogen-doped carbon(Fe₃O₄@NC-600)was successfully obtained by using a phase conversion method to achieve self-assembly and subsequently annealing.Fe₃O₄@NC-600 composite demonstrated higher specific capacity and better electrochemical stability than the pure Fe₃O₄nanoparticles and hard carbon derived from polyacrylonitrile.Under the current density of 0.2 A/g,Fe₃O₄@NC-600electrode can reach a high specific capacity of 981mAh/g after 500 cycles,even under the large current density of 1A/g,it can still maintain a high specific capacity of 632mAh/g after 900 cycles.(4)The columnar Fe C₂O₄·2H₂O material was synthesized by hydrothermal method using oxalic acid and potassium ferricyanide as raw materials,and then a porous columnar material with pores(Fe₃O₄-600)assembled from many interconnected Fe₃O₄nanoparticles was obtained after heat treatment.It was found that under the current density of 0.2 A/g,the specific capacity of 916 mAh/g was maintained after 250 cycles for Fe₃O₄-600 material,showing the excellent cycle reversible capacity.At a higher current density of 0.5 A/g,it can also maintain a better specific capacity of 630 mAh/g after a long cycling of 400 cycles,showing excellent cycle stability.(5)Thiosalicylic acid containing O and S elements was used as the organic ligands to coordinate with Mn²⁺in alkaline condition,and a fibrous material with large size coule be prepared using solvothermal method,then carbon doped MnO and MnS composite(MnO/MnS-C650)could be obtained under an appropriate heat treatment temperature.It can maintain the specific capacity of 1183 mAh/g at 0.2 A/g after 240 cycles,showing a high reversible capacity.Even at 0.5 A/g after 300 cycles,it can still have a specific capacity of 783 mAh/g,showing an excellent large multiplier cycle stability.