Surface modification and chemical stability of garnet LLZO solid electrolyte by ZnO coating through a facile and practical method

Abstract

All-solid-state lithium-ion batteries are promising choices to resolve high lithium-ion conductivity safety problems; however, they still have severe bottlenecks hindering their potential to be fully commercialized. This paper addresses interfacial resistance and a strong tendency to react with air and humidity. For this purpose, a Ga–Ta co-doped Li7La3Zr2O12 (LLZO) is dip-coated in an alcoholic zinc acetate solution to produce a thin zinc oxide (ZnO) layer after calcination to investigate any possible effects on reducing the interfacial resistance between electrolyte and anode. Furthermore, the effect of the ZnO layer on lithium deterioration (producing Li2CO3 or LiOH during air exposure) is examined by Fourier-transform Infrared spectroscopy (FTIR), Raman spectroscopy, field emission scanning electron microscopy (FESEM) and electrochemical impedance spectroscopy (EIS) after exposing both coated and uncoated LLZO to relatively humidified air for 30 days. Results indicate that LLZO electrolyte coated with ZnO in the thickness range of 400–600 nm obtained the highest ionic conductivity, i.e. 41% and 52% increase for Au/LLZO/Au and Li/LLZO/Li cells, respectively, compared to the pristine sample. After 30 days of exposure to humidified air, the coated electrolyte shows way better electrochemical results (0.62 mS/cm rather than 0.01 mS/cm for the uncoated sample) and a lower amount of Li2CO3 than the uncoated one.