| Graphite,as one of the most successful commercial anode for lithium-ion battery,still faces some problems such as low theoretical capacity(372 mAh/g).Therefore,finding and opening a new type of negative electrode material is still a meaningful work.Biomass has been extensively studied due to its wide range of sources,low cost,environmental protection,and renewables.Biomass-derived carbon materials have been widely used in some research fields such as water treatment,gas adsorption,and supercapacitors.In addition,as a anode for lithium ion batteries,transition metal oxides have a high theoretical specific capacity,but have poor cycle performance.In this paper,we prepared a composite material of biomass carbon and metal oxide,and studied its electrochemical performance.It is expected that the composite material is an ideal anode for lithium ion battery with good electrochemical performance.In the first part,we used corn stalk core as carbon source and FeCl3 as iron source.Fe3O4/C-1 was prepared by hydrothermal-high temperature carbonization method,and Fe3O4/C-2 was prepared by one-step carbonization method.The SEM image shows that the size of Fe3O4 particle in the 1-Fe3O4/C-1 composite prepared by 1 mol/L FeCl3 precursor was 1 μm,and the particle size of Fe3O4 in 1-Fe3O4/C-2 was 8 μm.According to the BET test results,the specific surface area of 1-Fe3O4/C-1 can reach 605.5 m2/g,while the specific surface area of 1-Fe3O4/C-2 is only 402 m2/g.Electrochemical test results show that 1-Fe3O4/C-1 exhibits excellent rate performance and cycle performance.The composite has a specific capacity of 960 mAh/g at a current density of 100 mA/g and the specific capacity can still maintained at 390.5 mAh/g after 500 cycles at a current density of 500mA/g,while the specific capacity of 1-Fe3O4/C-2 is only 220 mAh/g at a current density of 100 mA/g.The excellent electrochemical performance of 1-Fe3O4/C-1 is attributed to the fact that the larger specific surface area of corn stalk core carbon provides more loading sites for Fe3O4.At the same time,the size of Fe3O4 particles prepared by hydrothermal method is relatively small,which reduces the volume change during the charge and discharge process and the transport resistance of Li+.In the second part,we used onion skin as carbon source and Co(NO3)2·6H2O as cobalt source.The Co3O4/C composites were prepared by hydrothermal carbonization method.The effect of activation and different concentrations of Co(NO3)2·6H2O on the properties of composites were investigated.It can be seen from the SEM image that the thickness of the activated onion skin carbon is as thin as 0.80 μm,and the thickness of the onion skin carbon formed by direct carbonization is 1.2 μm.When the concentration of cobalt nitrate solution is 1 mol/L,the specific surface area of 1-Co3O4/C-1 can reach 702.2 m2/g,while the specific surface area of 1-Co3O4/C-2 is only 100.2 m2/g.Electrochemical test results show that 1-Co3O4/C-1 has the highest specific capacity of 1200 mAh/g at a current density of 100 mA/g,while 1-Co3O4/C-2 has only 502 mAh/g.After 500 cycles at a current density of 2000 mA/g,the specific capacity of 1-Co3O4/C-1 can reach 500 mAh/g,and the capacity retention rate is 70.4%.The AC impedance test results show that 1-Co3O4/C-1 has a smaller impedance than I-Co3O4/C-2.The excellent electrochemical performance of 1-Co3O4/C-1 is due to the fact that the KOH-activated carbon has abundant microporous mesopores and a large specific surface area,while the thin carbon layer also improves the electrical conductivity of the composite.In addition,a large amount of Co3O4 supported by the carbon material can store more Li+,which plays an important role in improving the specific capacity of the composite material. |
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