Flexible fluorine containing ionic binders to mitigate the negative impact caused by the drastic volume fluctuation from silicon nano-particles in high capacity anodes of lithium-ion batteries

Abstract

Novel ionic binders based on sulfonated polyether ether ketones and polysulfone backbones, bearing pendant lithiated fluorinated sulfonimide groups (SPEEK-PSI-Li and PSU-PSI-Li) were developed. Their performance in high performance silicon (Si) nano-particle anodes was studied in comparison with conventional binders such as lithiated sulfonated poly(ether-ether-ketone) containing fluorinated sulfonic acid side chains (SPEEK-PSA-Li), poly(vinylidene) difluoride (PVDF), sodium carboxymethyl cellulose (CMC) and alginate. Much superior to other anode binders, the ionic conducting SPEEK-PSI-Li binders could not only provide good adhesion properties, but also effectively reduce the over-potential during rapid charge and discharge cycles. When cycled at a current of 400 mA g⁻¹, these anodes could maintain above 2000 mA h g⁻¹ after 50 cycles. Even when cycled at a high current rate of 2000 mA g⁻¹, the anodes with SPEEK-PSI-Li binders could be cycled above 500 mA h g⁻¹ in 50 cycles. The superior performance of the novel SPEEK-PSI-Li binders could be attributed to their high cohesion capability, low solubility in electrolytes, high adaptability to volume fluctuation and high ionic conducting capability resulting from of the co-existence of flexible PEEK backbones, flexible fluorinated ether side chains, ionic transporting sulfonate groups, and pentadentate super ionic sulfonimide groups in the molecule structures.