Synthesis of garnet Li7–3(x + y)AlxGayLa3Zr2O12 powder by the Taylor reaction and electrochemical properties for all-solid lithium batteries

Abstract

Garnet-like Al and Ga co-doped LAGLZO (Li7–3(x + y)AlxGayLa3Zr2O12) (x, y = 0.00, 0.05, 0.20, 0.25) powders were prepared in a Couette-Taylor reactor via calcination. Increased Ga content (x = 0.00, y = 0.20) was shown to be associated with improved densification and smaller grains in the sintered pellet, showing the highest ionic conductivity of 1.13 × 10−3 S cm−1 at RT. The composite solid electrolyte (CSE) sheet is composed of LAGLZO and polyethylene oxide (PEO) polymer with LiClO4 showing an ionic conductivity of 4.52 × 10−4 S cm−1 at 70 °C. However, in the LSV and symmetric cell test, the addition of Ga to the CSE sheet increased the reactivity and over-potential against lithium metal. All-solid lithium batteries (ASLBs) were fabricated using a composite cathode, CSE sheet, and Li-metal anode. The initial capacity of the ASLB slightly increased in proportion to the increasing Ga content, but the capacity retention and rate characteristics decreased as a function of charge/discharge cycles. Capacity reduction was solved by the cell design comprised of the bi-layer CSE sheets (LGLZO-based CSE/LALZO-based CSE), which suppressed the reactivity with lithium metal. Thus, by applying a LGLZO-based CSE sheet to the cathode and LALZO-based CSE sheet on lithium metal in ASLBs, the initial cell capacity with NCM 424 was improved to over 130 mAh g−1 and a capacity retention of 93% was obtained after 50 cycles.