Synthesis And Electrochemical Performance Of Fluorine-doped Carbon Encapsulated MnO Nano-crystal

After the countries have suffered the pain of environmental pollution,it has been the development of clean energy storage device,reducing the consumption of fossil energy.Lithium ion batteries have been successfully used in mobile phones,laptops and wearable devices for the last two decades and the applications recently expands to electric vehicles.Therefore,it is necessary for us to develop the lithium ion battery technology and match the pace of the consumer electronics industry.The composition,structure and properties of electrode materials have a significant impact on lithium ion batteries.Transition metal oxides having a relatively high theoretical capacity is regarded as the promising anode candidates to replace the currently used graphite.Transition metal oxides also have some problems such as pulverization,poor electrical conductivity as well as poor cycle characteristics.To overcome those problems,much effort is focused on the preparation of nano-structured materials and carbon coating composites.In this paper,a simple synthetic method successfully prepared carbon-coated nano-structured transition metal oxides.A fluorinated carbon coated MnO nano-crystal with high crystallinity was achieved through a self-assembly route.Positive charged Mn²⁺ions were self assembled with the negative charged SO^3-end groups of perfluorosulfonic-acid?PFSA?ionomers.The synthesized materials were characterized through TEM,XPS and Raman spectroscopy and their electrochemical performances as the anode for lithium ion batteries were also investigated.Results are as follows:?1?We prepared PFSA/MxOy nanoparticles?M=Mn,Fe,Co and Ni?and tested the electrochemical performance and phase analysis to choose the proper transition metal oxides.The PFSA/MnO nanoparticles after carbonization showed the best performance,which had the initial charge capacity of 466 mAh/g under the current density of 100 mA/g.The capacity retention rate was 99.7%after 50 cycles of reversible charge and discharge.Phase analysis results show that four kinds of product only manganese and iron oxides were successfully synthesized,whereas cobalt,nickel oxide were reduced respectively in the carbonization process.In summary,manganese compound was confirmed as the most suitable material self assembled with PSFA.?2?Six kinds of content of manganese compound were added into PFSA.The six kinds of products were characterized and compared with each other to explore the best content of manganese compound.The specific capacity of MnO@FC nanoparticles was the highest when the molar ratio of C?provided by PSFA?to Mn?provided by Mn?Ac?2 4H2O?is 8:1.The size of MnO nano-crystals dispersed in PFSA solution was about 4 nm.?3?TEM,XPS,Raman spectroscopy and the electrochemical performance of MnO@FC nanoparticles illustrated that a 5 nm sized MnO nano-crystal encapsulated into a fluorine doped carbon material.And the ratio of F to C?C_F/C_C?in MnO@FC was found to be 5.6%.The resultant sample exhibited superior cyclic ability as an anode material in lithium ion batteries.The MnO@FC electrode still can demonstrate around 450 mAh/g capacity even after 10000 cycles under high current density of3.2A/g.