In-Situ Composites Of Manganese-Based Oxides/Sulfides And Carbon For Electrochemical Energy Storage

In this paper,we reported the synthesis of manganese-based oxides/sulfides and carbon nanocomposites through an in-situ growth strategy and further discussed their applications in electrochemical energy storage.The heteroatom-doped carbon matrix,on the one hand,enhances the electronic conductivity of the hybrid nanocomposites.On the other hand,it can effectively suppress the growth of inorganic solids into large particles during the material synthesis process and further prevent their aggregation during successive electrochemical cycling processes.More importantly,the physical confinement and heterogeneous interface interactions between manganese-based oxides/sulfides and carbon support are able to maintain the structural stability of the electrode during cycling,thereby guaranteeing the long-term cycling performance.The in-situ growth synthesis route involved in this work,simplifying the compounding process of inorganic solids with carbon matrix,is universal for the preparation of other transition metal oxides/sulfides.This paper mainly contains the following two research contents:Firstly,manganese monoxide nanoparticles embedded in nitrogen-doped carbon nanocomposites(MnO@NCN)were in-situ synthesized by a facile sol-gel method and then post annealing process.When investigated as anode materials for supercapacitors,the prepared MnO@NCN electrode achieved a high specific capacitance of 468.6 F g^-1at a scan rate of 2 m V s^-1.Besides,it exhibited excellent cycling performance with capacity retention of99.1%after 10000 cycles at a current density of 10 A g^-1.More importantly,the assembled asymmetric supercapacitor device(ASC),with MnO@NCN anode and nickel-cobalt layered double hydroxide(Ni Co-LDH)cathode,delivered a high energy density of 94 Wh kg^-1at a power density of 1731.6 W kg^-1,which is far beyond those ASCs based on the commonly adopted carbon anodes.Secondly,considering the advantages of MnO@NCN anode in supercapacitors and high energy density of batteries,we further prepared another MnO/carbon nanocomposite(MnO@NC)by self-propagating method.Due to slow kinetics of metal oxides,it exhibited poor performance as anode in sodium ion batteries.In view of the faster reaction dynamics and better conductivity of metal sulfides,the manganese sulfide and carbon nanocomposites(Mn S@NSC),obtained through sulfuration treatment of MnO@NC in argon atmosphere,were adopted as anode in sodium-ion batteries.According to the experimental results,the optimum sample,with a ratio of manganese nitrate and citric acid in the raw materials as 1:1.5,showed the best electrochemical performance.The optimum electrode achieved a capacity of283.7 m Ah g^-1at a current density of 0.1 A g^-1,and it retained 87.1%of initial capacity after700 cycles.