A multifunctional Janus layer for LLZTO/PEO composite electrolyte with enhanced interfacial stability in solid-state lithium metal batteries

Flexible composite solid electrolytes (CSEs) show great potential in high-energy all-solid-state lithium metal batteries owing to their easy fabrication, good electrochemical properties, and high safety. However, it remains challenging to achieve good interfacial compatibility between inorganic fillers and polymer, which affects lithium-ion transport and electrochemical performances of CSEs. Herein, we design a Li6.4La3Zr1.4Ta0.6O12 (LLZTO) filler coated with 3-methacryloxypropyltrimethoxysilane (MEMO) Janus layer for poly(ethylene) oxide (PEO) electrolyte (denoted as MEMO@LLZTO-PEO). We demonstrate the effect of MEMO coating on ionic transport of CSEs by the combined experimental and theoretical methods. The MEMO Janus layer facilitates uniform dispersion of filler in polymer as well as dissociates more lithium salt, which leads to much improved ionic conductivity of MEMO@LLZTO-PEO (2.16 × 10−4 S cm−1 at 30 ℃). Besides, MEMO@LLZTO could immobilize lithium salt anions via hydrogen bonding interactions and F–O chemical bonding, leading to good lithium-ion transference number (0.53) of MEMO@LLZTO-PEO. Moreover, we prepare a nonwoven fabric (NF)-supported CSE (denoted as MEMO@LLZTO-PEO-NF) to further improve the mechanical strength and safety of CSEs. The MEMO@LLZTO-PEO-NF shows great cyclability over 4000 h in a lithium symmetrical cell at a current density of 0.1 mA cm−2 (areal capacity: 0.1 mAh cm−2, 60 ℃). When used in all-solid-state Li/LiFePO4 batteries with a high active mass loading (>4 mg cm−2), MEMO@LLZTO-PEO-NF cell shows much-enhanced cyclability and rate capability at 60 ℃. This work also provides a new strategy to achieve good interfacial compatibility between inorganic fillers and polymer matrix in composite solid electrolytes for all-solid-state lithium batteries.