¹⁹F NMR investigation on the ratio of amorphous to crystal for the binder PVdF in Li ion battery

Abstract

$^{19}F$ NMR experiments were carried out to observe the change of the characteristics of the PVdF binder which is an auxiliary material of the lithium ion battery. PVdF has various crystalline or amorphous phases by thermal treatment. A mixture of cathode and auxiliary materials including PVdF was coated on aluminum foil as an electron collector and then subjected to thermal treatment at various temperatures. The overlapped $^{19}F$ NMR signals obtained from the various phases were separately convoluted into the respective phases, and it was found that there was a relative ratio change of these phases. In addition, the crystal and amorphous phase of PVdF was changed during the vacuum drying, which is the last step of the actual electrode manufacturing. It was observed that the relative amount of amorphous phase, which may affect the flexibility of the electrode or the wettability of the electrolyte, abruptly changes after a certain temperature.

Figure 2. Comparison between 19F NMR spectra of experimental results and deconvoluted spectra with crystal (alpha,beta), amorphous and defect (head to head, tail to tail).

Figure 1. ¹⁹F NMR spectra of heat treated PVdFs withtemperatures from 130 to 170 ℃.

Figure 3. 19F NMR spectra of heat treated PVdFs with temperatures from 130 to 170 ℃.

Figure 5. The ratio of the net amorphous andcrystal phases of PVdF for dried under vacuumand treated thermally.

Table 1. Relative integral intensities of deconvoluted ¹⁹F NMR spectra for heat treated PVdFs with different temperatures

Table 2. Relative integral intensities of 19F NMR spectra for PVdF dried under vacuum with different temperature