A polyethylene oxide based electrolyte enabled by the synergistic effect of active LiGaO2 filler and ionic liquid for superior lithium metal batteries

Polyethylene oxide (PEO) electrolytes have been extensively researched in solid-state batteries due to their excellent interface compatibility, high flexibility, and ease of machining. However, its practical application is still hindered by low ionic conductivity (∼10 −6  S cm −1 at room temperature) and a narrow electrochemical stability window. To settle these shortcomings, a PEO-based composite electrolyte enabled by active LiGaO 2 filler and 1-allyl-3-methylimidazolium bis(trifluoromethyl sulfonyl)imide (AMIm-TFSI) ionic liquid is constructed for lithium metal batteries (LMBs). Benefiting from the synergistic effect of LiGaO 2 filler and AMIm-TFSI ionic liquid, this composite electrolyte not only enhances the ionic conductivity (2.08 × 10 −3  S cm −1 ) and electrochemical window (5.2 V vs. Li + /Li) but also reduce the interfacial impedance. Furthermore, the Li//Li symmetric cells achieved an ultralong lithium deposition/stripping cycle over 1000 h at 0.1 mA cm −2 . The assembled solid-state LiFePO 4 //Li cell exhibit superior rate capability (164.2, 158.5, 154.8, 148.6, 119.4 mAh g −1 at 0.1, 0.2, 0.5, 1, and 2 C, respectively) and excellent cycling stability (147.3 mAh g −1 after 300 cycles at 0.2C). The X-ray photoelectron spectroscopy (XPS) analysis reveals that the composite electrolytes in situ form an inorganic-rich solid electrolyte interface layer. This work provides guidance on designing superior organic-inorganic composite electrolytes for LMBs.