A Single‐Ion Conducting Network as Rationally Coordinating Polymer Electrolyte for Solid‐State Li Metal Batteries

Solid state single-ion conducting polymer electrolytes (SSPEs) are one of the most promising candidates for long-life lithium-metal batteries. However, the traditional polyanion-type structure of SSPEs inevitably gives rise to insufficient conductivity and inferior mechanical stability, which limits their practical application. Herein, an interpenetrating single-ion network polymer (PTF-4EO) is fabricated by crosslinking lithium tetrakis(4-(chloromethyl)-2,3,5,6-tetrafluorophenyl)borate salt with tetraethylene glycol. The unique structure enables a PTF-4EO with weakly interacting anions and coordinating ether oxygen segments that functions as a high-performing SSPE, that delivers a high room-temperature conductivity of 3.53 x 10(-4) S cm(-1), exceptional superior lithium-ion transference number of 0.92, wide electrochemical window > 4.8 V, and good mechanical properties. Moreover, the resultant SSPE can directly participate in constructing a favorable Janus solid electrolyte interphase, which further enhances the interfacial stability of the metallic lithium anode. The as-assembled LiFePO4||Li solid batteries present prominent cycling stability, coulombic efficiency, and capacity retention over 200 cycles between 2.50 and 4.25 V. Furthermore, LiNi0.7Mn0.2Co0.1O2||Li pouch cells exhibit remarkable safety even under harsh conditions. This study thereby offers a promising strategy for SSPE design to simultaneously achieve high ionic conductivity and good interfacial compatibility toward practical high-energy-density solid-state lithium metal batteries.