Multiple Strategies Synthesis Of Ternary Metal Oxide/graphene Nanocomposites And Their Application As Anode Material For Li-ion Batteries

In recent years,under the background of global climate and ecological environment changes as the international mainstream issue,it is an inevitable trend of society development to transfer the traditional energy supply-consumption structure to a more clean,low-carbon emissions and higher efficiency of energy structure.With the improvement of new technology,the gap is reducing very quickly in the cost of energy consumption.Especially in recent years,solar,wind,sunlight costs decline significantly,and the cost of the new-energy is expected to be reduced by 20?25%in again in the next 5?10 years on the basis of the current electricity price,and the rapid decline in the cost aspects offers an opportunity for new-energy industry.At the same time,as the portable electric devices and new-energy vehicles develop,the requirements of energy storage equipment are claimed higher and higher.Lithium-ion batteries(LIBs)have attracted worldwide attention in virtue of their long-life span,high energy density and low environmental impact compared to other electrochemical energy carriers.In a variety of electrode materials,metal oxides have been extensively investigated as advanced anodes because of their numerous merits,such as high theoretical capacity,low cost and good safety,and has broad application prospects.However,the low conductive and the large volume expansion/shrinkage of metal oxides during the lithiation/delithiation processes hinders the actual application severely.Therefore,to counter the question existing in metal oxides electrode,we work out some corresponding strategies to enhance the cycling stability and rate performance.The main contents are as following:(1)We present a novel strategy to prepare MnCo2O4/graphene composites on nickel foam.TEM analysis reveals that high density of MnCo2O4 nanoparticles of 5?10 nrn are uniformly anchored on graphene nanosheets.The MnCo2O4/graphene-anchored Ni foams are used as binder-free integrated anodes for lithium ion batteries(LIBs)and exhibit superior lithium-storage performance.The MnCo2O4/graphene composites exhibit high cycling stability(868 mAh g-1 at 100 mA g-1)and good rate capacity(607 mAh g-1 at 1600 mA g-1)as anode materials for LIBs.The prominent electrochemical performance is associated with the synergistic effects of 3D porous Ni foam and graphene,which promote electron transfer and buffer the large volume fluctuation of metal oxides during the lithiation/delithiation progress.(2)CoFe2O4 quantum dots/N-doped graphene(CoFe2O4 QDs/N-G)composites have been successfully fabricated through a facile strategy involving a hydrothermal process and subsequent calcination at high temperature.Uniform nanoparticles with high density are homogeneously anchored on the surfaces of graphene sheets.The CoFe2O4 QDs with a distribution within 4?12 nm can be observed clearly,and there is no apparent aggregation of CoFe2O4 QDs on the graphene nanosheets.The CoFe2O4 QDs/N-G obtained as an anode material for LIBs presents an initial discharge capacity of 1616 mAh g-1 and maintains a reversible capacity of 1223 mAh g-1 after 90 cycles at a current of 100 mA g-1.The gradual capacity increase with cycling results primarily from the formation of Co3-during the electrochemical process.After being cycled at various rates for 90 cycles,the capacity can recover to 1239 mAh g-1 when the current is switched to 100 mA g-1.This superior lithium-storage performance can be attributed to the quantum and size effects of CoFe2O4 quantum dots and the excellent electrochemical properties of N-doped graphene.(3)Three-dimensional(3D)carbon-coated ZnFe2O4 nanospheres/N-doped graphene aerogels(ZnFe2O4@C/N-G)have been synthesized via a facile hydrothermal method.The obtained ZnFe2O4@C hierarchical nanospheres with a size tistribution of 150?210 nm are uniformly encapsulated within the graphene aerogels matrix.The ZnFe2O4@C/N-G composites as anode materials for Li-ion batteries demonstrate a high initial discharge capacity of?1176 mAh g-1 with an initial coulombic efficiency of-71.1%at a rate of 100 mA g-1.Moreover,a significantly enhanced reversible capacity of 952 mAh g-1 is retained after 100 cycles.After being cycled at various rates for 100 cycles,the capacity can reincrease to 955 mAh g-1 when the specific current returns back to 100 mA g-1.The improved electrochemical performance is attributed to the unique architectures of the carbon layer(2?4 nm)and 3D porous N-doped graphene aerogels.