Ultrathin single-ion conducting polymer enabling a stable Li|Li1.3Al0.3Ti1.7(PO4)3 interface

NASICON-type Li1+xAlxTi2−x(PO4)3 (LATP) solid electrolytes have attracted great attention because of their high ionic conductivity, wide electrochemical stability window, pronounced chemical resistance, and low cost. However, the chemical instability of LATP against metallic lithium (Li0) poses a major challenge and hinders its application in solid-state lithium batteries. Herein, an ultrathin polysiloxane-based single-ion conductor (PSiO) serves as multifunctional protection interlayer to enhance the interfacial stability between LATP and Li0. PSiO effectively blocks the direct contact between Li0 and LATP, regulates the homogeneous Li+ flux at the Li|electrolyte interface, promotes the intimate contact between PSiO and Li0 by forming Si − O − Li bonds, and generates an LiF-enriched Li|electrolyte interphase. As a result, it enables more than 2,000 h of stable cycling in symmetric PSiO@Li‖PSiO@Li cells and superior rate capability and cycling stability in high-energy PSiO@Li‖LiNi0.88Co0.09Mn0.03O2 cells. The realization of well performing 2-layer bipolar stacked cells eventually demonstrates the great potential of this approach.