Solvent-Phobic and Ionophilic Carboxylated Polythiophene Layer for Fluoride-Rich Cathode Electrolyte Interphase

One focal area of contemporary organic mixed ionic-electronic conductor (OMIEC) research relates to utilization of dual-conductive properties to enhance the ion/electron transfer kinetics for energy storage applications. Insight regarding OMIEC response toward the electrolyte anion and solvent used in lithium-ion batteries (LIBs), however, is limited. Here, for the first time, the solvent-phobic and ionophilic (SP-IP) properties of the OMIEC, poly[3-(potassium-4-butanoate)thiophene-2,5-diyl] (P3KBT), are revealed through comprehensive evaluation and characterization. The solvent-phobic characteristics arise from the cooperation of dispersive interaction, polar interaction, and hydrogen-bonding between P3KBT and electrolyte solvent. The ionophilic nature is driven by electrostatic interactions between P3KBT side chain carboxylate groups and LiPF₆, and the reversible electrochemical doping/de-doping of the polythiophene backbone with PF₆^⁻. The SP-IP properties induce formation of a LiF-rich, Li₂CO₃-limited cathode electrolyte interphase (CEI) layer when a P3KBT coating layer is applied to the active material surface, significantly improving half-cell life to over 1500 cycles at 2C.