Polyvinylidene fluoride (PVDF) is a fluoropolymer which consists of vinylidene fluoride as a monomer. Conventionally, it is widely used material in electrode preparation as a binder between active carbon material and the current collector. However in this work, we propose the use of PVDF as a polymer precursor to carbon. In literature, PVDF was used as precursor for carbon with ~20% yield.1 However, this yield was increased to ~70% by dehydrofluorination of PVDF prior to pyrolysis.2,3
In our present work, we first carried out dehydrofluorination followed by pyrolysis at different temperatures (900, 1200 and 1400 ⁰C respectively) to obtain the hard carbon as characterization by field emission scanning electron microscopy, X-ray diffraction, Raman spectroscopy and high resolution transmission electron microscopy. Later, electrochemical performance of these hard carbons pyrolyzed at different pyrolysis temperature was investigated at different current densities.
Experimental Section:
PVDF powder was dehydrofluorinated in NaOH and Tetra-n-butylammoniumbromide solution. Dehydrofluorinated powder was pyrolyzed in inert atmosphere at different final pyrolysis temperature. Slurry made of this carbon was coated over stainless steel foil and dried for 12 h in a vacuum oven prior to cell packing in argon atmosphere glove box. Electrochemical performance was studied using glavanostat/potentiostat.
Results and discussions:
Figure 1: (a,b) HRTEM images of CDI-1400 at different magnifications; (c) Comparison of cycling behaviour at 0.1 C rate for carbonized samples for different temperature
TEM images (Figure 1a and 1b) clearly reveals that particle size is 290 nm and inside the each spherical particle, there are disordered areas consists of randomly arranged smaller crystallites of graphene. From this, we can conclude that carbon derived from PVDF precursor is a hard carbon.
From Figure 1c, we observe that the sample pyrolyzed at 1400 ⁰C exhibited higher reversible capacity (297 mAh/g) than the other two samples (pyrolyzed at 900 ⁰C and 1200 ⁰C) after 11 cycles of charge-discharge at 0.1 C rate. The coulombic efficiency was found to be more than 94 % after 11 cycles for all three samples. A detailed analysis on dehydroflorination and charge discharge experiments at different current densities will be presented at conference. Cyclic voltammetry and impedance studies will also be presented to support the cyclic stability and capacity retention values.
References:
1. T. Zheng et al., Electrochem. Soc. 142, 2581–2590 (1995)
2. Jatuphorn et al., Journal of Metals, Materials and Minerals. 18, 57-62, (2008).
3. Seok-Min Hong et al., RSC Adv. 4,58956-58963 (2014).