Lithiated Nafion-garnet ceramic composite electrolyte membrane for solid-state lithium metal battery

Abstract

Abstract Single-ion conducting solid polymer electrolytes are expected to play a vital role in the realization of solid-state Li metal batteries. In this work, a lithiated Nafion (Li-Nafion)-garnet ceramic Li6.25La3Zr2Al0.25O12 (LLZAO) composite solid electrolyte (CSE) membrane with 30 µm thickness was prepared for the first time. By employing X-ray photoelectron spectroscopy and transmission electron microscope, the interaction between LLZAO and Li-Nafion was investigated. It is found that the LLZAO interacts with the Li-Nafion to form a space charge layer at the interface between LLZAO and Li-Nafion. The space charge layer reduces the migration barrier of Li-ions and improves the ionic conductivity of the CSE membrane. The CSE membrane containing 10 wt% LLZAO exhibits the highest ionic conductivity of 2.26 × 10−4 S cm−1 at 30 °C among the pristine Li-Nafion membrane, the membrane containing 5 wt%, 20 wt%, and 30 wt% LLZAO, respectively. It also exhibits a high Li-ion transference number of 0.92, and a broader electrochemical window of 0–+4.8 V vs. Li+/Li than that of 0–+4.0 V vs. Li+/Li for the pristine Li-Nafion membrane. It is observed that the CSE membrane not only inhibits the growth of Li dendrites but also keeps excellent electrochemical stability with the Li electrode. Benefitting from the above merits, the solid-state LiFePO4/Li cell fabricated with the CSE membrane was practically charged and discharged at 30 °C. The cell exhibits an initial reversible discharge specific capacity of 160 mAh g−1 with 97% capacity retention after 100 cycles at 0.2 C, and maintains discharge specific capacity of 126 mAh g−1 after 500 cycles at 1 C. The CSE membrane prepared with Li-Nafion and LLZAO is proved to be a promising solid electrolyte for advanced solid-state Li metal batteries.