Surface properties enhancement of battery separator by micro-plasma treatments

The aim of this work is to test the wettability enhancement of a low-wetting and low-cost commercial polymer separator by cold microplasma treatments. Liquid and gas ammonia are tested as precursors in a pulsed microreactor at low pressure. Two modes of plasma producing are used, i.e., with and without bias. Optical emission spectroscopy, contact angle technique, and cycling tests are performed to characterize the process and the separator. Best results are obtained with liquid ammonia precursor without bias (contact angle between water and a polyethylene separator being 10° ± 2° compared to 111° ± 2° without any treatment). Cycling tests of lithium half-cells incorporating plasma-treated separator show drastic improvements to capacity retention at high rates (after 100 cycles at a 2C rate, the discharge capacity of a Li₄Ti₅O₁₂ is almost three times higher, i.e., 38 mA h g⁻¹ and 113 mA h g⁻¹ with an untreated separator and a treated one, respectively).