Preparation and Characterization of Silicon-Carbon-Graphite electrode as anode material for lithium ion batteries

Preparation and Characterization of Silicon-Carbon-Graphite electrode as anode material for lithium ion batteries
Lithium ion battery; anode; silicon-carbon composite
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Thermal pyrolysis of sucrose dispersed with nanosized silicon at 800°C in nitrogen atmosphere and addition of graphite particles produced silicon-carbon (SC) and silicon-carbon-graphite (SCG) composite electrodes for lithium storage batteries. The mass losses of carbon in silicon/carbon (35/65, 20/80 wt.%) were estimated values of 55.9 and 74.1 % by thermo gravimetric analysis. However, the practical carbon contents using element analysis were evaluated 30.1 and 47.6 %, respectively. Two main peaks via raman spectra were observed at around 1350 and 1580 cm-1, which are designated as the D and G band, respectively. As the ID/IG ratio increases, the defect structure increases and the degree of graphitization becomes less. In addition, the X-ray diffraction showed that no peaks corresponding to carbon can be seen. The raman and X-ray diffraction showed that the structure was amorphous. The electrochemical performance of SC and SCG were tested with different carbon contents and addition of graphite. All cell test performed charge-discharge cycling to nearly 100 % depth of discharge and did not limit the insertion capacity or the lower potential range. SC composites have much better capacity retention than pristine micro and nano size silicon materials. The remarkable improvements of cycle stability accommodated the volume change of the silicon and good conductivity of the active material. However, the initial coulombic efficiency (IQE) of SC electrode was decreased still 51.8% compared with pristine micro and nano silicon electrodes. The existence of lot of amorphous silicon probably provides for trapping site of Lithium ions during the charge (lithiation)-discharge (delithiation). In order to compensate irreversible capacity, SCG electrode was fabricated as addition of graphite. The IQE of SCG electrode was increased about 20% because of compensated trap site without variation of cycle retention.
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