Preparation And Electrochemical Performances Of Porous Transition Metal Oxide Materials

Transition metal oxides have been focused on as one of the most promising anode materials for LIBs because of their high theoretical specific capacity(>700 mAh g-1),natural abundance,environmentally friendly,and easy preparation.However,most metal oxides are semiconductor,meaning they have lower conductivity than carbon anodes and experience a conversion reaction during the(de)insertion process.Thus,the combination of poor electrical conductivity,low initial Coulombic efficiency and large volumetric expansion results in poor cycling stability and rate capability,which impose restrictions on their commercial implementation.Based on this,this research synthesizes porous materials with appropriate components and special structures.And we investigate the relationships of porous structure and composites for electrochemical behavior.The main research contents and results are as follows:1.Porous NiO nanorods are synthesized through a thermal treatment of Ni-MIL-77 as precursor in air.When evaluated as anode materials for LIBs,porous NiO nanorods exhibit excellent electrochemical performance owing to plenty of pores and nanosized building blocks.At a current density of 100 mA g-1,an initial discharge capacity of 743 mAh g-1 is obtained,and a high reversible capacity is still maintained as high as 700 mAh g-1 even after 60 charge-discharge cycles,and exhibiting good cycling stability.2.A NiAl-layered double hydroxide(LDH)is vertically grown on RGO by the microwave-assisted method without any surfactant or template.The NiAl-LDH/RGO is used as precursor to synthesize sandwich-like porous Al2O3/RGO anchoring NiO nanocomposite(NiO-Al2O3/RGO)by subsequent calcination and etching process.When used as anode materials for LIBs,at the current density of 500 mA g-1,a stable capacity as high as 704 mAh g-1 is obtained after 200 cycles.As for the NiO-Al2O3/RGO nanocomposites,Al2O3 acts as stabilizer,avoiding agglomeration and pulverization of active materials during cycling process.RGO regards as conductive agent and buffer agent,not only improving the electrical conductivity of the materials,but also alleviating the volume change during(dis)charge process.3.The precursor of MnCO3-CNTs@TiO2 microspheres are prepared by two-step co-precipitation method.Then,MnCO3-CNTs@TiO2 is prepared by a new and efficient approach for in-situ carbon modification by acetylene treatment.The proposed design is shown to significantly improve the stability and Coulombic efficiency(CE)of metal(oxide)anodes.The initial Coulombic Efficiency of MnO-CNTs@TiO2-C is 73%,and at a harsh rate of 5000 mA g-1,a capacity of 389 mAh g-1 can be maintained after 2000 cycles.The proposed oxide anode design is combined with nickel-rich cathode to make a full-cell battery that works at high voltage,the capacity retention can be maintained at 78.4%after 200 cycles at the high rate of 0.5 C.The structural characteristics of the nanocomposites are as follows:The CNTs penetrate the oxide particles and buffer volume change,while enhancing electrical conductivity.Meanwhile,the external TiO2-C shell serves as a transport pathway for mobile metal ions(e.g.,Li+),and acts as a protective layer for the inner oxides by reducing the electrolyte/metal oxide interfacial area and minimizing side reactions.4.A novel three-dimensional Cu(OH)2 nanorod arrays is in-situ grown on the copper foil by chemical oxidation,and then following the calcination of precursor under argon atmosphere,obtaining 3D porous Cu/Cu2O current collector.The corresponding electrochemical properties are as follows:A high Coulombic efficiency above 98.6%and long-term cycle life over 380 cycles are demonstrated at the current density of 0.25 mA cm-2 in the model of Cu/Cu2O | Li half-cell.Besides,an extremely long lifespan over 1700 h and a low polarization voltage(13 mV)are also demonstrated in a symmetrical cell using the lithium plated Cu/Cu2O electrode(Cu/Cu-Li2O-Li).The great features of as-presented electrode are further studied versus LiFePO4 and sulfurized polyacrylonitrile cathode,respectively,where extraordinary rate capability and cycling stability are both affirmed.The structural characteristics of the 3D porous current are as follows:A robust combination of Cu2O and Cu foil benefits for the fast transportation of lithium ions/electron;abundant channels provide space for lithium deposition;the Cu2O arrays can be in-situ reduced(Cu and Li2O)further for a high electron transfer capability and then providing sufficient electroactive site,and inhibiting electrolyte decomposition.