Synthesis,Modification And Electrochemical Performances Of Manganese Oxides

This paper is based on the electrolytic manganese dioxide?EMD?,chemical manganese dioxide?CMD?and the manganese oxide transition metal oxides which are applied as research object of the cathode material and anode material of lithium primary battery and lithium-ion battery,respectively,and research and discussion has carried on the material synthesis,modification,crystal structure,micro structure and electrochemical properties and mechanism.Experiment scheme and specific content are as follows:?1?The commercial electrolysis manganese dioxide and commercial graphite fluoride were used as raw material.Different annealing temperature and annealing time are carried on the electrolysis manganese dioxide.XRD,TGA and FESEM technology had been used to characterize the crystal structure and microstructure of the electrolysis manganese dioxide.The results show that XRD indicate the manganese dioxide is gamma type before calcinations;its crystal structure changed gradually after calcination at different temperature.The TGA results show that the EMD decomposition at 540 degrees,and generate Mn2O3.In SEM images,there are no obvious change between before and after calcinations,and microstructure of samples were presented the irregular small nanoparticles,and the particle size of samples are less than 100 nm.Constant exile electric system and the electrochemical workstation are use to test the electrochemical properties of electrolytic manganese dioxide which are used as cathode material for Lithium primary battery.The experimental results show that EMD have the higher discharge specific capacity when calcined at 350 degree for 8h;The EMD calcined at 350 degree for 8h have smaller charge transfer impedance.The XRD,TGA,EA and FESEM and TEM techniques are used to characterize the crystal structure,thermal stability,and the degree of fluoride?the ratio of fluorine atoms and carbon atoms?of commercial graphite fluoride?CF0.77?.The result shows that crystal type has great change,crystallinity reduced and crystal disorder increases of Graphite fluoride?CF0.77?compared with graphite;TGA test results show that the decomposition of electrolytic manganese dioxide happened at 540 degrees,and decomposition of graphite fluoride happened at 580 degrees.EA test results show that the ratio of fluorine atoms and carbon atoms of graphite fluoride is 0.77.In the SEM images,graphite fluoride?CF0.77?presents a amorphous granular of micron level;In the TEM images,obvious layered structure can be observed.Constant exile electric system and the electrochemical workstation are use to test the electrochemical properties of CF0.77 which are used as cathode material for Lithium primary battery.The experimental results show that the discharge specific capacity of graphite fluoride decreased slightly with the increase of current density.Optimized EMD?350-8?and CF0.77 are mixed at different mass ratio,and constant exile electric system and the electrochemical workstation are use to test the composite materials which are mixed at different mass ratio,used as the cathode material for lithium primary battery.The results show that composite material express the excellent and improve the electrochemical performance at the mass ratios of 2:5 and 1:6.Composite materials express the Synergy at some certain mass ratios;the discharge specific capacity of composite material is higher than the separate discharge specific capacity of EMD?350-8?and CF0.77 at the mass ratios.?2?At room temperature,potassium permanganate?KMnO₄?and manganese sulfate?MnSO₄?were used as raw materials,and chemical precipitation was used to prepare the pure MnO2 and MnO2 which are doped with Cr,Co and Ni ions.The XRD,TGA,and TEM were used to characterize the crystalline structure,thermal stability and morphology of manganese dioxide samples which prepared by chemical precipitation method.The result shows that MnO2?0?is?-MnO2,and the MnO2 which were doped with Cr and Ni ions both are ? type while MnO2?Co?is ? type.MnO2?0?is the nanoflowers-like structure which is composed of nanosheet with the diameter of 10nm.MnO2?Cr?is the nanorod-like structure with the diameter of 20-30 nm.MnO2?Co?is also the nanorod-like structure with the diameter of 50-60 nm which are larger than MnO2?Cr?.MnO2?Ni?is stacked of small nanosheet.Constant current charge-discharge and electrochemical workstation were used to test the electrochemical properties of MnO2?0??MnO2?Cr?,MnO2?Co?and MnO2?Ni?which are prepared by chemical precipitation method and used as cathode materials for LIBs.The experimental results show that MnO2 samples expressed improved electrochemical performance after doping.MnO2?Ni?showed the most excellent electrochemical performance,and the discharge specific capacity retain at 106 mAh g^-1 after 50 cycles at the current density of 100mA g^-1.At different temperature and different reaction time,ammonium persulfate??NH₄?2S₂O₄?and manganese sulfate?MnSO₄·H2O?were used as raw materials,and it take on hydrothermal method to prepared the chemical manganese dioxide.The XRD,TGA,and TEM were used to characterize the crystalline structure,thermal stability and morphology of manganese dioxide which prepared by hydrothermal method.The result shows that MnO2(120^-12)which prepared at 120 ? for 12 h is a type while the others are ? type,and crystallinity of the?-MnO2 treated at 150 0C for 24 h is higher than MnO2(120^-24).MnO2(120^-12)material sample is micro thorn ball like made of nanowires;MnO2(120^-24)?MnO2(150^-12)and MnO2(15 0^-24)are all nanorod-like structure but with slightly different diameter,respectively are 60-80nm,50-60 nm,50-60nm.Constant current charge-discharge and electrochemical workstation were used to test the electrochemical performances of MnO2(120^-12),MnO2(120^-24),MnO2(150^-12)and MnO2(150^-24)which are prepared by hydrothermal method and used as cathode materials for LIBs.The experimental results show that MnO2(120^-24)and MnO2(150^-12)showed excellent electrochemical performances.MnO2(120^-24)sample expresses higher discharge specific capacity,while MnO2(150^-12)sample shows much more the stability of cycling.?3?The P-MnO2/carbon nanotubes?CNTs?nanocomposites were prepared by hydrothermal method?150 ? for 24 h?with Mn2+ and S₂O82-as reactants in the presence of different content of CNTs.The crystalline structure,thermal stability,the content of carbon and morphology of the products were characterized by XRD,TGA,EA,SEM and TEM.The experimental results show that the pure MnO2 is ? type,and the additions of different amount of CNTs have no influence on the crystalline structure of composite materials.The TEM and SEM results show that MnO2/CNTs nanocomposites are composed of MnO2 nanorods with the diameters 60-80 nm and CNTs with the diameters 40-50 nm which intertwined tightly.Constant current charge-discharge and electrochemical workstation were used to test the electrochemical performances of composite materials.The experimental results show that the discharge specific capacity of ?-MnO2??-MnO2/CNTs^-1??-MnO2/CNTs^-2 are 88?180 and160mAh g^-1 after 100 cycles at a large current density of 1C(308 mA g^-1).The ?-MnO2/carbon nanotubes?CNTs?nanocomposite was prepared by chemical precipitation method at room temperature for 24h)with Mn2+ and MnO₄-as reactants in the presence of CNTs?20 wt%?.The crystalline structure,thermal stability,the content of carbon and morphology of the products were characterized by XRD,TGA,EA,SEM and TEM.The experimental results show that the pure MnO2 prepared by chemical precipitation method is ?type.The ?-MnO2 is the self-assembly nano flower-like structure with the size of 200-300 nm which is formed by nanosheet.Constant current charge-discharge and electrochemical workstation were used to test the electrochemical performances of composite material.The experimental results show that though ?-MnO2/CNTs have a high initial discharge specific capacity,?-MnO2 and ?-MnO2/CNTs show a inevitable attenuation at a large current density of 1C(308mA g^-1).Meanwhile,?-MnO2/CNTs was prepared by chemical precipitation-hydrothermal method at 120 ? for 24h with Mn2+ and MnO₄-as reactants in the presence of CNTs?20 wt%?as same.The crystalline structure,thermal stability,the content of carbon and morphology of the products were characterized by XRD,TGA,EA,SEM and TEM.The experimental results show that the pure MnO2 prepared by chemical precipitation-hydrothermal method is y type;?-MnO2 is nano particle-like structure with 30-60 nm,and small amount of nanorod-like structure can be observed.Constant current charge-discharge and electrochemical workstation were used to test the electrochemical performances of composite material.The experimental results show ?-MnO2/CNTs expresses excellent performance of embedding and taking off of lithium ions.At the same current density and the same cycles,?-MnO2/CNTs showed the improved circulation performance and higher discharge specific capacity.?4?Mn3O₄ samples were prepared by hydrothermal method at different temperature for 24 h with?CH₃COO?2Mn·4H2O and NH₃ H2O as reactants.The crystalline structure,thermal stability and morphology of the products were characterized by XRD,TGA,SEM and TEM.The experimental results show that Mn3O₄ prepared at different temperature are all Hausmannite,syn type?JCPDS 24-0734?.The sample prepare at 160 ? also appear the characteristic peak of a-MnO2;And the sample prepare at 160? also appear the characteristic peak of ?-Mn3O₄.Constant current charge-discharge and electrochemical workstation were used to test the electrochemical performances of materials.The experimental results show these four electrodes,cycling for 100cycles at the current density of 100mA g^-1,expressing different capacities.Mn3O₄?140?expressed the most outstanding performance,the specific discharge capacities retain at 513mAh g^-1 after 50 cycles and 324mAh g^-1 after 100 cycles,respectively.In addition,Mn3O₄?140?expressed the excellent electrochemical performance at the large current performance test.Mn3O₄?140?/CNTs was prepared by same method at 140 ? for 24h with Mn?CH₃COO?2·4H2O and NH₃ H2O as reactants in the presence of CNTs.The crystalline structure,thermal stability,the content of carbon and morphology of the products were characterized by XRD,TGA,EA,SEM and TEM.The experimental results show that the addition of CNTs did not change the crystalline structure of MnO₄?140?.Mn3O₄?140?and CNTs dispersed well in the composite material,and Mn3O₄?140?show smaller diameter of nano-particles.Constant current charge-discharge and electrochemical workstation were used to test the electrochemical performances of material.The experimental results show that the electrochemical performances of the Mn3O₄?140?composited with CNTs improved greatly.The discharge capacities of Mn3O₄?140?/CNTs retain at 1055 mAh g^-1 after 50 cycles and 515 mAh g^-1 after 100 cycles,respectively.In addition,Mn3O₄?140?/CNTs expressed the excellent electrochemical performance at the large current performance test.