Role of SiO_x in rice-husk-derived anodes for Li-ion batteries

The present study investigated the role of SiO_x in a rice-husk-derived C/SiO_x anode on the rate and cycling performance of a Li-ion battery. C/SiO_x active materials with different SiO_x contents (45, 24, and 5 mass%) were prepared from rice husk by heat treatment and immersion in NaOH solution. The C and SiO_x specific capacities were 375 and 475 mAh g^-1, respectively. A stable anodic operation was achieved by pre-lithiating the C/SiO_x anode. Full-cells consisting of this anode and a Li(Ni_0.5Co_0.2Mn_0.3)O₂ cathode displayed high initial Coulombic efficiency (~ 85%) and high discharge specific capacity, indicating the maximum performance of the cathode (~ 150 mAh g^-1). At increased current density, the higher the SiO_x content, the higher the specific capacity retention, suggesting that the time response of the reversible reaction of SiO_x with Li ions is faster than that of the C component. The full-cell with the highest SiO_x content exhibited the largest decrease in cell specific capacity during the cycle test. The structural decay caused by the volume expansion of SiO_x during Li-ion uptake and release degraded the cycling performance. Based on its high production yield and electrochemical benefits, degree of cycling performance degradation, and disadvantages of its removal, SiO_x is preferably retained for Li-ion battery anode applications.