Polyethylene oxide/garnet-type Li6.4La3Zr1.4Nb0.6O12 composite electrolytes with improved electrochemical performance for solid state lithium rechargeable batteries

Next generation lithium batteries require new electrolytes with good safety, excellent ionic conductivity, high electrochemical stability and good cycling performance. Herein, we first report a solid composite polymer electrolyte comprises of Li6.4La3Zr1.4Nb0.6O12 fillers and polyethylene oxide matrix. The ionic conductivity of the solid composite electrolyte is significantly improved to 1.4 × 10−3 S cm−1 (60 °C) and the electrochemical window is enhanced to 5.2 V, respectively, by incorporation of Li6.4La3Zr1.4Nb0.6O12 powder at a weight ratio of 0.5:1 with respect to polyethylene oxide. The solid batteries employing the composite electrolytes are able to work at room temperature and have a capacity retention of 99% after cycle. The performance improvement is primarily due to the combined functions of each component in the composite: (i) the incorporation of fillers effectively decreases the crystallinity of PEO, providing more amorphous region for ion conduction; (ii) Li6.4La3Zr1.4Nb0.6O12 serves as a fast ion conductor in the composite and enhance the electrochemical stability; (iii) the polymer matrix forms intimate surface contact with fillers and electrodes, reducing the bulk and interfacial resistance. The composite polymer electrolyte in this work would be a competitive alternative for the next generation solid state lithium rechargeable batteries.