Currently, enormous efforts have been focused on the fabrication of flexible power storage due to their potential applications in wearable electronics such as Internet of Things (IoT), medical implants, RFID tags, smart cards, sensors etc.¹ In general, a graphite has been used as an anode material for Li-ion batteries. However, the graphite electrode delivers a maximum theoretical capacity only 372 mAh.g^-1. One-dimensional carbon-based materials, carbon nanotubes (CNTs), have been extensively investigated as anode material due to its remarkable properties such as an excellent Li-ion storage capacity, lightweight, good electronic conductivity and excellent mechanical properties ^2,3. Indeed, carbon nanotube electrodes exhibit significantly higher reversible charge-discharge capacity than the intercalated graphite ⁴. To fabricate an all-solid-state Li-ion microbatteries, solid electrolytes such as polymer electrolyte has drawn lots of attention in order to facilitate the miniaturization of microelectronic devices and to avoid the leakage risks. More recently, our group has reported the electrochemical synthesis of p-sulfonated poly (allyl phenyl ether) (SPAPE) as polymer electrolyte with an excellent cycling performance ⁵.

In this work, we carried out the electrodeposition process by cyclic voltammetry technique to increase the electrode/electrolyte interface with enhanced electrochemical performance. Fig. 1a and b show the SEM images obtained from top surfaces of the CNTs tissue before and after electropolymerization for 10 cycles. The CNTs tissue appears as a web of disoriented continuous curved nanotubes, with an average diameter of 20 - 30 nm. The pristine CNTs tissues were used as working electrode for the electropolymerization of p-sulfonated allyl phenyl ether in cathodic conditions with the potential windows -0.9 V to -1.8 V vs. Ag/AgCl and a scan rate of 20 mV/s.

Fig. 1 SEM images of CNTs tissue before electropolymerization a) and after electropolymerization for 10 cycles b).

Fig. 2a and b show the areal capacity versus cycle number of the pristine CNTs and the electropolymerized CNTs as anodes. The electrochemical tests were performed in a half-cell against Li foil using the two-electrode Swagelok cells. The cell was cycled at different C-rates in a potential window 0.01 – 2 V vs. Li/Li⁺. The large irreversible capacity value at the first cycle is attributed to electrolyte reduction and the formation of a solid electrolyte interface (SEI) layer on the surface of CNTs electrode ⁶. In any case, the reduction of irreversible capacity of CNTs electrode still needs further investigation. After the first cycle, a reversible capacity value of ~300 µAh.cm^-2 (~815 mAh.g^-1) could be obtained at 1C rate over 50 cycles, which is much higher than the previous works reported elsewhere ^7–9. The cycle life performance tests show that the CNTs anode could achieve a good electrochemical performance in terms of rate capability and cycling stability.

Fig. 2. Discharge capacity versus cycle number of the pristine CNTs and the electropolymerized CNTs electrodes at a) 1C rate and b) at multi C-rates

References

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