Preparation Of Nickel (Cobalt) And Bismuth Based Electrode Active Materials And Their Electrochemical Performances

In view of the safety concern and high cost of organic battery systems such as lithium-ion batteries,and the strong toxicity of lead-acid battery and nickel//cadmium aqueous batteries,it is imperative to explore and develop novel aqueous rechargeable batteries.Because of the advantages such as relatively low redox reaction potential range(-1.0-0 V)in KOH aqueous electrolyte,multi-electron faradic reaction,non-toxicity and low cost,bismuth is deemed as an excellent anode active material for aqueous rechargeable batteries.Based on the current investigation on aqueous rechargeable Ni//Bi batteries and the fundamental research on battery-type active materials of aqueous hybrid supercapacitors,a series of nickel(cobalt)based highly active battery-type electrode materials were prepared based on micromorphology modification and structure engineering.Then novel aqueous rechargeable batteries(NiMoO₄@NiCo-layered double hydroxide//Bi₂O₂CO₃,Co_xNi_1-xMoO₄@NiCo-layered double hydroxide//Bi₂MoO₆,CoNi-CoNiO₂@NiCo-layered double hydroxide//Bi₂O₃,Co_0.5Ni_0.5MoO₄//Bi₂WO₆ and Co_0.5Ni_0.5MoO₄@rGO//Bi₂MoO₆@rGO),were assembled with those nickel(cobalt)based active materials,various bismuth based anode active materials and 6 M KOH aqueous electrolyte.The specific contents of this thesis are presented as follows:(1)Assembly of NiMoO₄@NiCo-layered double hydroxide//Bi₂O₂CO₃ aqueous batteries and their electrochemical performanceThe NiMoO₄ grown on nickel foam was adopted as the 'core' materials to further grow NiCo-layered double hydroxide by the hydrothermal method,where that NiMoO₄ was optimized and prepared at the molar ratio(hexamethylenetetramine to Ni(CH₃COO)₂·4H₂O)of about 6:1.The optimized cathode active materials NiMoO₄@NiCo-layered double hydroxide heterostructure nanoarrays exhibit excellent electrochemical performances,such as high specific capacity up to 323.9 m Ah/g at the current density of 1 A/g and good rate capability of 67.8%in the current density range of 1-10 A/g.Highly porous Bi₂O₂CO₃microspheres were prepared as anode active materials by a hydrothermal method,which display a specific capacity of 186.3 m Ah/g at 0.5 A/g,high rate capability of 90.1%in 0.5-10A/g and excellent cycling performance.The aqueous rechargeable battery assembled with above cathode and anode active materials delivers the energy density and power density of46.7 Wh/kg and 720 W/kg at 1 A/g.(2)Assembly of Co_xNi_1-xMoO₄@NiCo-layered double hydroxide//Bi₂MoO₆ aqueous batteries and their electrochemical performanceSubstitution of Co for Ni species of Co _XNi_1-XMoO₄(0?X?1)as 'core' materials and growing time of NiCo-layered double hydroxide onto the 'core' materials were optimized systematically.The optimized cathode active materials Co_0.5Ni_0.5MoO₄@NCLDH-12 show a decent specific capacity of 386.7 m Ah/g at 1 A/g and good rate capability of 64.9%at 15 A/g.The Bi₂MoO₆ with well-developed pore structure was synthesized as anode active materials by a solvothermal method,which demonstrates a high specific capacity of 163.2 m Ah/g at 1A/g,good rate capability of 79.6%in 1-15 A/g and excellent cycling performance.The aqueous rechargeable battery assembled with above cathode and anode active materials delivers the energy density and power density of 41.5 Wh/kg and 369.3 W/kg at 0.5 A/g.(3)Assembly of CoNi-CoNiO₂@NiCo-layered double hydroxide//Bi₂O₃ aqueous batteries and their electrochemical performanceCoNi-CoNiO₂@NCLDH heterostructure nanoarray was prepared by using CoNi-CoNiO₂as the backbone materials and NiCo-layered double hydroxide as 'shell' materials.CoNi-CoNiO₂@NCLDH exhibits outstanding specific capacities of 249.7 and 112.0 m Ah/g at1 and 20 A/g,respectively.The capacity retention after 6500 cycles is about 31.6%.The excellent electrochemical properties of CoNi-CoNiO₂@NCLDH are closely related to its micromorphology and structure.And the pores between these nanosheets contribute to the diffusion of electrolyte ions and enhancing the utilization efficiency of active materials.As the anode active materials,the 'cookie' -like Bi₂O₃ with loose stacking states exhibit excellent electrochemical properties,such as high specific capacities of 266.7 and 203.3 m Ah/g at 2and 20 A/g,respectively,and acceptable capacity retention of 62.6%after 1900 cycles at 15A/g.The aqueous rechargeable battery assembled with above cathode and anode active materials delivers the energy density and power density of 34.8 Wh/kg and 691.0 W/kg at 1A/g.(4)Assembly of Co_0.5Ni_0.5MoO₄//Bi₂WO₆ aqueous batteries and their electrochemical performanceThe cathode active materials of Co_0.5Ni_0.5MoO₄ with powder form were prepared by a hydrothermal method coupled with annealing treatment without any growing substrates,which present highly porous microsphere morphology consisting of 'ribbon'-like nanosheets intertwined with each other.The Co_0.5Ni_0.5MoO₄ microspheres show an outstanding specific surface area of 293 m²/g.The cathode active materials present a specific capacity of 113.2m Ah/g at 1 A/g,rate performance of 51.8%in 1-15 A/g,and capacity retention of 48.5%after4600 cycles at 15 A/g.Porous Bi₂WO₆ microspheres assembled from nanosheets were prepared as anode active materials,which afford a specific capacity of 179.2 m Ah/g at 1 A/g,rate capability of 74.7%in 1-20 A/g,and capacity retention of 57.2%after 1500 cycles at 15A/g.The aqueous rechargeable battery assembled with above cathode and anode active materials delivers the energy density and power density of 35.8 Wh/kg and 331.8 W/kg at 0.5A/g.(5)Assembly of Co_0.5Ni_0.5MoO₄@rGO//Bi₂MoO₆@rGO aqueous batteries and their electrochemical performanceIn order to improve the utilization efficiency of cathode and anode active materials(Co_0.5Ni_0.5MoO₄and Bi₂MoO₆),hybridizing them with reduced graphene oxide(rGO)were performed separately.The introduction of rGO can change the micromorphology and pore structure of those active materials,and improve the specificities.The optimized cathode active materials Co_0.5Ni_0.5MoO₄@rGO-10 exhibit a specific capacity of 150.5 m Ah/g at 1 A/g,and superior rate capability of 73.6%in 1-15 A/g.The optimized anode active materials Bi₂MoO₆@rGO-25 demonstrate the average specific capacities of 198.0 and 150.3 m Ah/g at1 and 20 A/g,respectively.The aqueous rechargeable battery assembled with above cathode and anode active materials delivers the specific capacities of 75.4 and 40.0 m Ah/g at 0.5 and10 A/g,respectively.And the energy density and power density at 0.5 A/g are about 53.1Wh/kg and 351.6 W/kg,respectively.The two aqueous rechargeable battery models connected in series can light up one red LED bulb,indicating this kind aqueous rechargeable battery system possesses a promising application prospect.