Synthesis Of Cobalt Oxide Nanocomposites As Anodes For Lithium-Ion Batteries

As one of the most promising energy conversion and storage device,rechargeable lithium-ion batteries（LIBs）have been developed in an attempt to meet the rising global energy demand.The transition metal oxides with high specific capacities have been explored to be alternative options to substitute commonly used graphitic materials as anodes for LIBs.Typically,Cobalt oxide（CoO）has been regarded as an attractive anode candidate on account of its low cost and high theoretical specific capacity(716 mAh g^-1).Nevertheless,the practical application is still hindered by their inherently low electronic conductivity and drastic volume expansion during lithiation/delithiation processes,which have negative impacts on the LIBs performance.Accordingly,it is imperative to engineer a new transition metal oxides-based nanomaterial with optimized structures for the preferable performance LIBs,include:reversible capacity,cycle performance,rate capability.The main contents of this thesis are as follows:（1）Firstly,the nanorod CoO precursors and nanorod copper oxide（CuO）precursors were prepared,and the two precursors were calcined after mixing with graphene oxide.The CoO and CuO nanoparticles with a high density are uniformly dispersed on the reduced graphene oxide（rGO）.As anode materials for LIBs,the CoO/CuO/rGO nanocomposites delivered an initial discharge capacity of1732.4 mAh g^-1 and a stabilized capacity of 1364.6 mAh g^-1 at a current density of200 mA g^-1 after 100 cycles.With increased current density to 1000 mA g^-1and2000 mA g^-1,the nanocomposites retained high reversible capacities of 602.7 mAh g^-1and 423.5 mAh g^-1 after 1000 cycles,respectively.（2）Co（NO₃）₂?6H₂O was dissolved in the Tris buffer solution（pH=8.5）by one pot method to form a homogeneous solution,followed by the gentle addition of dopamine and polymerize at room temperature.During this process,Co ions are incorporated into the PDA film via coordination to hydroxyl and amino group of dopamine to form Co²⁺-PDA precursor.During the subsequent pyrolysis carbonization process,Co ions oxidize and transform into CoO nanoparticles while PDA converts into the N-doped carbon layer with large mesopores.The as-synthesized Co/CoO@N-C nanocomposite anode manifest a greatly improved initial capacity of 1497 mAh g^-1 and retain a high reversible value of 1115 mAh g^-1 at a current density of 200 mA g^-1 after 125 cycles.When cycled at a higher current density of 500 mA g^-1,a high discharge capacity of 532.1 mAh g^-1 is retained even after 500 cycles.（3）Firstly,the CoO precursor Co（CO₃）_0.5（OH）?0.11H₂O was prepared through a hydrothermal route,the precursor was dissolved in a Tris buffer solution with pH=8.5to form a homogeneous solution,then slowly added with dopamine and polymerize at room temperature.The synthesized PDA was coated on the surface of CoO precursor andcalcinedinargonatmospheretoobtainthefinalproduct Co/CoO@N-Ccomposites.At the current density of 200 mA g^-1,the initial discharge capacity is 1163.67 mAh g^-1.The initial discharge capacity are 828.88 mAh g^-1and649.86 mAh g^-1 at the current density of 500 and 1000 mA g^-1,respectively.