Using high‐HFP‐content cathode binder for mitigation of heat generation of lithium‐ion battery

Abstract

Summary We investigate the effects of thermally sensitive binder (TSB) on the temperature increase of lithium‐ion battery (LIB) coin cell subjected to severe mechanical abuse. The TSB is poly(vinylidenefluoride‐co‐hexafluoropropylene) (PVDF‐HFP), similar to conventional poly(vinylidenefluoride) (PVDF) binder but with a significant hexafluoropropylene (HFP) content. The testing data show that by using TSB, the peak temperature increase of nail‐penetrated LIB coin cell can be reduced by 20% to 40%, attributed to the softening of TSB that begins from ~80°C. The cycling performance of the LIB cells is also characterized. This research sheds light on the development of thermal‐runaway mitigation techniques.

Effects of macromolecular configuration of thermally sensitive binder in lithium‐ion battery

“…When soaked in electrolyte, the polymer becomes less stiff; the melting temperature range is 15–20 °C lower, and the heat absorption is much reduced. More importantly, the electrolyte‐soaked B03 is softened at ∼50 °C, which explains the poor cycle lives of LIB cells based on pristine B03 . Clearly, the as‐received B03 offers relatively low strength, low solvent resistance, and low thermal stability.…”

“…Clearly, the as‐received B03 offers relatively low strength, low solvent resistance, and low thermal stability. The as‐received B03 has a relatively broad M w distribution, which is likely one of the reasons of the fast degradation rate of LIB coin cells . As the charge–discharge cycles continue, the macromolecules of the lowest M w lead to aggressive local swelling, so that the overall LIB cell capacity decreases.…”

“…When the BPO content increases to 10 wt %, X‐10 based LIB cells exhibit a better cycle life than reference cells. As the BPO content further rises to 20 wt %, however, the degradation rate of X‐20 based cell is increased to higher than that of X‐2 based cell, but still much lower than that of the cells based on pristine B03 . It is clear that crosslinking helps stabilize the binder phase and reduce swelling, so that the LIB cells are much more stable than B03‐based ones.…”

“…Molecular weight, M w , is a vital factor that dominates thermal, mechanical, and swelling properties of polymers . Previous testing data indicated that the solvent resistance of B03 was too low while the softening temperatures of B01 and B02 were too high . Therefore, if M w of B03 can be increased or M w of B01 or B02 can be reduced, the balance between thermal sensitivity and swelling might be enhanced.…”

“…The thermally sensitive binder (TSB) is designed to fail at elevated temperature (∼110 °C) and to disintegrate the electrode components. Our previous testing results showed a 40% reduction in peak temperature increase in nail penetration test on coin cells; however, the cycle life of these TSB‐based LIB was poor, which was attributed to the premature swelling of the investigated TSB, poly(vinylidene fluoride‐ co ‐hexafluoropropylene) (PVDF‐HFP). The HFP component renders the binder phase thermally sensitive yet also more amorphous and more susceptive to electrolyte attack.…”