Study On The Manganese-based Layered Materials For Alkali Metal Ion Insertion/Extraction

Layered manganese-based material is widely researched due to the good electrochemical performance of manganese oxides and the merits of manganese such as abundance and low cost.In this dissertation,the concept of composite is used to guide the material design and modification for the chosen materials of NaNi_1/3Co_1/3Mn_1/3O₂,Na_xMnO₂,while the composition of materials is tuned and the electrochemical performances are enhanced.The possibility and the versatility for the alkali metal ion?Na⁺,Li⁺?storage are studied,with doping or substitution as supplementary means to improve the discharging performance.?1?The high-temperature solid state method was used to realize the combination between Li2MnO3 and NaNi1/3Co1/3Mn1/3O2 effectively and the phase compositions were controlled by the ingredient proportion.X-ray diffraction test result shows that the main peak of two phases shifts to lower angle,thus the expanded interlayer spacing with the increasing of Li2MnO3content.And in this way,P2/O3 structure is formed.The microscopic particles of composite material are relatively uniform,and maintains after the cycles of high cut-off charging voltage without obvious intergranular cracking or pulverization,indicating improved interface stability.The electrochemical performances for the as-prepared composite materials present elevated reversible specific capacity and enhanced rate capability ascribed to the activation of Li₂MnO₃.Also,the cyclic voltammetry test verifies the enhanced electrochemical activity after combination with Li₂MnO₃.Electrochemical impedance spectrum results demonstrate that the material 0.4Li₂MnO₃·0.6NaNi_1/3Co_1/3Mn_1/3O₂ with optimal ratio holds small charge transfer resistance with better interfacial stability and higher diffusion coefficient.?2?Quantum chemical calculation results indicate that the requirement of metal site vacancy formation is low enough to be realized in experiment,and the partial nickel substitution for lithium in the mixed layer?Li,Mn?can reduce the extration voltage of lithium,so we predict that the modification can reduce the irreversible capacity loss in the initial cycle.Based on that,0.5Li_2-xNi_x/2MnO₃·0.5NaNi_1/3Co_1/3Mn_1/3O₂?x=0,0.5?materials were designed and modified,using organic co-precipitation method for preparation,and the electrochemical performances for hybrid lithium ion battery cathode?vs Li?were studied.XRD results indicate that the as-prepared materials are well crystallized,and the extraction of sodium form electrode after the initial charge.Galvanostatic charge and discharge test show that the composite materials 0.5Li_2-xNi_x/2MnO₃·0.5NaNi_1/3Co_1/3Mn_1/3O₂ deliver excellent electrochemical performance when used as hybrid lithium ion battery cathode.The modification of nickel substitution for Li2MnO3improves discharging plateau and the capacity contribution from high voltage part with reduced polarization during charging and elevated coulombic efficiency of the first cycle.The cyclic voltammetry test certifies the capacity change and redox potential shift for the initial three cycles.?3?Under flow of inert gas,novel sodium manganese oxide was prepared by facile method,with tetrabutyl titanate?TBOT?as ingredient for titanium doping and introduction of crystal water.Through Ti-substitution for Mn site to inhibit the multiple plateaus upon cycling with phase transformation,employing interstitial water to improve the sodium ion diffusion,the optimal doping amount?5%?was selected by their electrochemical performances.According to the XRD result,the ratio between P2 phase and Birnessite phase can be controlled by control of tetrabutyl titanate amount.The existence of trace amount of crystal water was certified by Fourier transform infrared spectroscopy?FTIR?and thermogravimetric/differential thermal analysis?TG/DTA?.Scanning electron microscopy?SEM?observation for as-prepared materials indicates that the reactants were effectively dispersed,thus the particles of product were nanosized.Electrochemical performance tests show that the multiple phase transition were suppressed upon cycling,the charging and discharging curves got smoothed for modified material,and the rate capability were greatly enhanced especially for at high-rate currents with elevated reversible capacity.Through electrochemical impedance spectrum?EIS?to study the dynamic parameters of material,the results demonstrate that the modified material holds lower charge transfer resistance and higher sodium ion diffusion coefficient compared to pristine sodium manganese oxide.?4?By rinsing product with water after the preparation of sodium manganese oxide,Birnessite-type sodium manganese oxide was gathered.Adding graphene oxide during the synthesis process to form composite,its performance as lithium ion battery anode and the effect for addition of GO was studied.From the XRD result,the diffraction peak intensity of product become weaker with formation of MnO phase when the GO content is higher.Transmission electron microscope?TEM?observation demonstrate that the pristine material contains large particle size with severe agglomeration when the GO modified material receive good dispersion effect.Through FTIR test,the absorption peaks representing oxygen-containing functional group of C=O,C-O bond at 1736 cm^-1,1224 cm^-1,1046 cm^-1 disappear for modified material compared to as-prepared GO,indicating the reduction of GO during high-temperature process.With optimal amount of GO addition?BG-3,MnO₂:GO=2:3?,rate capability is improved with lower capacity fade at high-rate currents,achieving higher reversible capacity and better stability compared to pristine material?BG-0?.Higher redox activity and reversibility are testified by cyclic voltammetry.Moreover,EIS results indicate that Birnessite-type sodium manganese oxide holds small charge transfer resistance when used as lithium ion battery anode.Also,the GO modified material shows even lower charge transfer resistance,and remains relatively stable upon cycling.