High-Performance 3-D Fiber Network Composite Electrolyte Enabled with Li-Ion Conducting Nanofibers and Amorphous PEO-Based Cross-Linked Polymer for Ambient All-Solid-State Lithium-Metal Batteries

Solid electrolytes have gained attention recently for the development of next-generation Li-ion batteries since they can fundamentally improve the battery stability and safety. Among various types of solid electrolytes, composite solid electrolytes (CSEs) exhibit both high ionic conductivity and excellent interfacial contact with the electrodes. Incorporating active nanofibers into the polymer matrix demonstrates an effective method to fabricate CSEs. However, current CSEs based on traditional poly(ethylene oxide) (PEO) polymer suffer from the poor ionic conductivity of PEO and agglomeration effect of inorganic fillers at high concentrations, which limit further improvements in Li+ conductivity and electrochemical stability. Herein, we synthesize a novel PEO based cross-linked polymer (CLP) as the polymer matrix with naturally amorphous structure and high room-temperature ionic conductivity of 2.40 × 10−4 S cm−1. Li0.3La0.557TiO3 (LLTO) nanofibers are incorporated into the CLP matrix to form composite solid electrolytes, achieving enhanced ionic conductivity without showing filler agglomeration. The high content of Li-conductive nanofibers improves the mechanical strength, ensures the conductive network, and increases the total Li+ conductivity to 3.31 × 10−4 S cm−1. The all-solid-state Li|LiFePO4 batteries with LLTO nanofiber-incorporated CSEs are able to deliver attractive specific capacity of 147 mAh g−1 at room temperature, and no evident dendrite is found at the anode/electrolyte interface after 100 cycles. A highly ionic-conductive 3-D fiber network composite solid electrolyte is introduced based on Li-ion conducting nanofibers and amorphous poly(ethylene oxide) (PEO) cross-linked polymer. With the reinforcement of Li0.3La0.557TiO3 (LLTO) nanofibers, the continuous 3D conduction network formed within the polymer matrix greatly enhances the electrochemical and mechanical properties of resultant composite solid electrolytes. Consequently, the lithium dendrite is effectively controlled after long cycles, and the all-solid-state Li|LiFePO4 prototype cells demonstrate excellent cycling stability at room temperature.