Functionalized Polyethylene Separators with Efficient Li-Ion Transport Rate for Fast-Charging Li-Ion Batteries

Fast-charging lithium-ion batteries (LIBs) are the key to solving the range anxiety of electric vehicles. However, the lack of separators with high Li⁺ transportation rates has become a major bottleneck, restricting their development. In this work, the electrochemical performance of traditional polyethylene separators was enhanced by coating Al₂O₃ nanoparticles with a novel green binder. This binder was synthesized by grafting allyl alcohol ethoxylates (APEG) onto the backbone of poly(acrylic acid) in water solution. The presence of abundant hydroxyl and ether groups, along with a three-dimensional structure, not only ensures a homogeneous and stable physical structure for the separator but also functionalizes the separator-electrolyte interface to facilitate Li⁺ transport. Consequently, the separator exhibits a high electrolyte uptake of 95.16% and a good peeling strength of 1.243 N cm^-1. The electrolyte in the separator has an excellent Li⁺ transference number of 0.69. Especially, a cell with the optimized binder (with the APEG ratio of 10%) exhibits a 34% and 40% increase in capacity at 10 C compared to cells using polyvinylidene fluoride and lithium polyacrylate (PAALi) binders, respectively. These promising results could guide the development of more advanced binder materials for fast-charging LIBs.