Fabrication Of Manganese Oxide Nanocomposites And Their Applications In Supercapacitors

The rapidly expanding field of supercapacitor offers a promising way to overcome safety,cost,and power density limitations of lithium ion battery technology.As an important family,Mn-based oxides,typically MnO₂,are the most commonly used electrode materials in supercapacitor?SCs?,but some drawbacks?e.g.a low conductivity and a low crystallinity?limit their application especially in the high energy density supercapacitor field.Among the efforts of building efficient Mn-based supercapacitors,electrode materials with rational nanostructured designs have offered major improvements in performance over the past several years.Thus,MnO₂ based materials were chosen as research subject to improve the electrochemical performance.The research contents of this thesis are as follows:?1?In order to study the influence of synthesis conditions on the electrochemical performance,intricate morphology of MnO₂ from nanorods to nanospheres have been designed and prepared through a facile hydrothermal synthesis method.The phase changing process were characterized and analyzed by SEM,XRD and combined with electrochemical performance.It is found that the flower like ?-MnO₂ nanospheres were acquired at 140? for 6 h and exhibited a superior average specific capacitance of 192.7 F g^-1 at 0.5 A g^-1 and over 94.6%of the original specific capacitance retention after 1000 cycles,indicating it was a promising electrode material.?2?To effectively fabricate and use MnO₂ in supercapacitors,a graphene/polyvinylidene fluoride?GO/PVDF?composite binder has been designed and fabricated.The 5%CBE shows higher specific capacitance(220 F g^-1)than the 5%PBE(202 F g^-1)at 0.5 A g^-1 with an identical amount of graphene,which is physically mixed in the manufacturing process of electrodes.The specific capacitance of 220 F g^-1 can be obtained with graphene mass ratios up to 5 wt%.In addition,the 5%CBE shows excellent cycling stability that is over 90.1%of the initial specific capacitance retained after 1000 cycles.?3?A flower-like MnO₂ nanocomposite embedded in nitrogen-doped graphene?NG-MnO₂?is fabricated by a hydrothermal method.It is a mesoporous nanomaterial with a pore size of approximately 0.765 ca3 g^-1 and specific surface area of 201.8 m2 g^-1.NG-MnO₂ exhibits a superior average specific capacitance of 220 F g^-1 at 0.5 A g^-1 and a preferable capacitance of 189.1 F g^-1,even at 10 A g^-1.After 1000 cycles,over 98.3%of the original specific capacitance retention of the NG-MnO₂ electrode is maintained,and it can even activate a red light emitting diode?LED?after being charged,which indicates that it has excellent cycling stability as an electrode material.