Double Ionic-Electronic Transfer Interface Layers for All-Solid-State Lithium Batteries.

Large-scale implementation of all-solid-state lithium batteries is impeded by the physical limitations of the interface between the electrode and solid electrolyte; specifically, high resistance and poor stability, as well as poor compatibility with Li+ migration. We report double ionic-electronic transfer interface layers grown at electrode-electrolyte interfaces by in situ polymerization of 2,2'-bithiophene in polyethylene oxide (PEO) electrolyte. For all-solid-state LiFePO4 ∥PT-PEO-PT∥Li cells, the formation of a conductive polythiophene (PT) layer at the cathode-electrolyte interface resulted in an at least sevenfold decrease in interface resistance, and realized a capacity retention of about 94 % after 1000 cycles along with a lower polarization voltage under a rate of 2 C. The mixed ionic-electronic conductive layers imparted superior interface stability and contact while keeping good compatibility with the Li anode.