Construction of SnO2 buffer layer and analysis of its interface modification for Li and Li1.5Al0.5Ge1.5(PO4)3 in solid-state batteries

SnO2 layer between Li1.5Al0.5Ge1.5(PO4)3 (LAGP) and lithium anode was prepared through simple scratch-coating process to improve interface properties. The physical phase, morphology, and electrochemical properties of Li/SnO2/LAGP structure were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and electrochemical analytical methods. It was found that SnO2 layer effectively improved the interface stability of LAGP and lithium anode. The prepared Li/SnO2/LAGP/SnO2/Li symmetric cell exhibited a large critical current density of 1.8 mA cm−2 and demonstrated excellent cycling characteristics. The polarization voltages of symmetric cell were 0.1 V and 0.8 V after 1000 h of cycling at current densities of 0.04 mA cm−2 and 0.5 mA cm−2, respectively. Li/SnO2@LAGP/LiFePO4 solid-state full cells were also assembled, exhibiting a discharge specific capacity of 150 mAh g−1 after 200 cycles at 0.1C with capacity retention rate of 96 %. The good interface properties of Li/SnO2/LAGP structure are attributed to the transformation of SnO2 layer into a buffer layer containing Li2O, Sn0, and LixSny alloy during cycling process, which effectively inhibits the reduction reaction between LAGP and lithium anode.