Water-soluble fluorine-free poly(ionic liquid) borate binders for Li-ion battery cathodes

Abstract

The development of efficient, eco-friendly lithium-ion battery (LIB) technologies necessitates alternative binder materials to replace conventional polyvinylidene fluoride (PVDF). Five novel water-soluble poly(ionic liquid) (PIL) binders based on poly(diallyldimethylammonium) (PDADMA) with borate counteranions. The binders—PDADMA–C4B, PDADMA–C3B-A, PDADMA–C3B-B, PDADMA–PyrB, and PDADMA–TriB were synthesised and characterised for thermal stability, electrolyte uptake, adhesion, and electrochemical performance. Among these, PDADMA–C4B demonstrated superior properties, including high thermal stability (>200 °C), significant electrolyte uptake (303 %), and low internal resistance, leading to improved cycling performance of LIB. At high C-rates, PDADMA–C4B outperformed PVDF, maintaining structural integrity and higher discharge capacities. Surface analyses confirmed minimal degradation, underscoring the durability of the PDADMA–borate binders. These results highlight PDADMA–C4B as a sustainable, high performance alternative to fluorinated binders, promoting advancements in LIB technology.