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Recently, applications for lithium-ion batteries (LIBs) have expanded to include electric
vehicles and electric energy storage systems, extending beyond power sources for portable electronic devices. The power sources of these flexible electronic devices require the creation of thin,
light, and flexible power supply devices such as flexile electrolytes/insulators, electrode materials,
current collectors, and batteries that play an important role in packaging. Demand will require the
progress of modern electrode materials with high capacity, rate capability, cycle stability, electrical
conductivity, and mechanical flexibility for the time to come. The integration of high electrical
conductivity and flexible buckypaper (oxidized Multi-walled carbon nanotubes (MWCNTs) film) and
high theoretical capacity silicon materials are effective for obtaining superior high-energy-density
and flexible electrode materials. Therefore, this study focuses on improving the high-capacity,
capability-cycling stability of the thin-film Si buckypaper free-standing electrodes for lightweight and
flexible energy-supply devices. First, buckypaper (oxidized MWCNTs) was prepared by assembling
a free stand-alone electrode, and electrical conductivity tests confirmed that the buckypaper has
sufficient electrical conductivity (10−4
(S m−1
) in LIBs) to operate simultaneously with a current
collector. Subsequently, silicon was deposited on the buckypaper via magnetron sputtering. Next,
the thin-film Si buckypaper freestanding electrodes were heat-treated at 600 ◦C in a vacuum, which
improved their electrochemical performance significantly. Electrochemical results demonstrated that
the electrode capacity can be increased by 27/26 and 95/93 µAh in unheated and heated buckypaper
current collectors, respectively. The measured discharge/charge capacities of the USi_HBP electrode
were 108/106 µAh after 100 cycles, corresponding to a Coulombic efficiency of 98.1%, whereas
the HSi_HBP electrode indicated a discharge/charge capacity of 193/192 µAh at the 100th cycle,
corresponding to a capacity retention of 99.5%. In particular, the HSi_HBP electrode can decrease the
capacity by less than 1.5% compared with the value of the first cycle after 100 cycles, demonstrating
excellent electrochemical stability.
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