Preparation,electrochemical Performance Of Two Dimension Layered Manganese-based Oxides,and Design Of Flexible Devices

With the rapid development of human society,fossil fuels were depleted rapidly then caused serious environmental pollution.Exploring new energy with merits of renewable and sustainable,or designing efficient energy storage and conversion devices are the best ways to solve problems mentioned above.Supercapacitors as a type of promising energy storage device,has been attracted researchers'attention because of its ultralong cycle life,low cost and environmentally friendly.Moreover,compared with batteries,supercapacitors have a higher power density.Unfortunately,a lower energy density of supercapacitors hinders its further application in the energy storage field.Thus,researchers focus on improving potential window or/and capacitance to improve energy density of supercapacitors.Many reports reported that a higher contribution of diffusion capacitance that originated from electrochemical reaction could increase the supercapacitors'potential window and capacitance to increase the energy density further.In this thesis,the two dimension(2D)layered manganese-based oxides were synthesized,then the diffusion capacitance contribution was optimized by controlling unique phase transformation,fabricating core-shell structure,doping heteroatom and introducing defects to enhance electrochemical performance and gain a higher energy density.Furthermore,in order to meet the demands of flexible electronic industries,various of flexible supercapacitors were designed and fabricated finally.The main progresses were obtained from this thesis are following:(1)Two dimension ?-MnO₂ nanosheets(2D?-MnO₂)was directly synthesized by one-step hydrothermal reaction,then the unique phase transformation of 2D?-MnO₂ was studied.Two dimension?-MnO₂(2D?-MnO₂)with mixed structure that consisted of tunnel structure and layered structure was obtained by the phase transformation of 2D?-MnO₂.Compared with 2D?-MnO₂ and 1D?-MnO₂,2D?-MnO₂ exhibits the best electrochemical performance.The capacitance of 2D?-MnO₂ is 267.0 F g^-1,and it could retain 84.4%of initial capacitance after 5000cycles.Moreover,the diffusion contribution of 2D?-MnO₂ retains 49.7%during electrochemical process.An aqueous symmetrical supercapacitor(2D?-MnO₂-SC)was assembled by using 2D?-MnO₂ as electrode,2D?-MnO₂-SC presents a capacitance of 267.0 F g^-1 and a high potential window 0-2.0 V,the highest energy density and power density are 38.9 Wh kg^-1-5.8×10~4 W kg^-1 respectively.(2)The two dimension layered double metal oxide Mn-NiLDO-C was designed by heat treatment of layered double metal hydroxide Mn-Ni LDH with low temperature.The effects of ratio of Mn/Ni and thickness of carbon shell for morphology and electrochemical performance were studied.Mn-NiLDO-C presents the best electrochemical performance finally.The capacitance of Mn-NiLDO-C is4729 mF cm^-2,after 5000 cycles,Mn-NiLDO-C could hold a capacitance retention of92.1%.Moreover,the diffusion contribution of Mn-NiLDO-C reaches 89.7%.A battery-supercapacitor hybrid device(BSH)was assembled by Mn-NiLDO-C as positive electrode and activated carbon as negative electrode,BSH has a high voltage of 2.0 V,and keeps 281.6 F g^-1 at 1 A g^-1,thus BSH has a satisfied energy density of78.2 Wh kg^-1.(3)The Cu doped layered double metal oxide with porous carbon shell coated Cu-Mn-CoLDO-C was synthesized by heat treatment of Cu-Mn-Co LDH.The effects of ratio of Mn/Co,amounts of Cu dopant and thickness of carbon shell for morphology and electrochemical performance were studied.Cu-Mn-CoLDO-C presents more appropriate diffusion contribution during electrochemical process.It holds 73.4%at 1 m V s^-1 and keeps 18.3%at 100 m V s^-1.Thus,Cu-Mn-CoLDO-C exhibits more excellent electrochemical performance.The capacitance of Cu-Mn-CoLDO-C reaches 5028.7 mF cm^-2,after 5000 cycles,Cu-Mn-CoLDO-C maintains96.5%of initial capacitance.An all-solid flexible asymmetrical supercapacitor(SAS)was fabricated using Cu-Mn-CoLDO-C as positive electrode and prepared Fe₃O₄-C as negative electrode,the capacitance of SAS is 540.8 mF cm^-2 finally.Besides,SAS has an ultrawide potential window of 0-2.4 V and ultrahigh energy density of 243.1?Wh cm^-2.(4)The F-MnO_2-x@PPy ultralong nanobelts was obtained with F doped and PPy coated.The effects of amounts of F dopant and thickness of PPy shell for morphology,mechanical properties and electrochemical performance were studied.The F-MnO_2-x@PPy paper-like electrode was fabricated subsequently.F-MnO_2-x@PPy paper-like electrode has a superior mechanical property:6.4%elongation at break with 6.7 MPa tensile strength.The capacitance of F-MnO_2-x@PPy paper-like electrode is 268.6 mF cm^-2,after 5000 cycles,F-MnO_2-x@PPy paper-like electrode could retain 96.8%of initial capacitance.The paper-like asymmetrical solid-state supercapacitor(ASS)was assembled by F-MnO_2-x@PPy paper-like electrode as positive and V₂O₅ paper-like electrode(consisted of V₂O₅ ultralong nanobelts)as negative,ASS has a considerable mechanical property,the elongation at break increases to 17.7%with a tensile strength of 1.7 MPa.Furthermore,the highest area energy density of ASS is 40.7?Wh cm^-2 and volume energy density is 1.8 m Wh cm^-3.(5)Sulfide-based oxides Mn-CoLDO-x S with different S contents were synthesized by Mn-CoLDO with different levels of sulfidation.The effect of S contents and defects forming for electrochemical performance were discussed.A plenty of sulfur vacancies were detected in Mn-CoLDO-2S that with a S content of nearly 50%,thus Mn-CoLDO-2S exhibits the best electrochemical performance.The capacitance of Mn-CoLDO-2S reaches 1863.5 F g^-1,and retains 93.6%of initial capacitance after 5000 cycles.An in-plane supercapacitor(SPS)which employed Mn-CoLDO-2S as electrode materials was designed by a template method.The capacitance of SPS is 201.9 mF cm^-2,the highest area energy density is 55.0?Wh cm^-2 and the highest volume energy density is 0.6 m Wh cm^-3.