Turning waste into wealth: Li2CO3 impurity conversion into ionic conductive and lithiophlic interphase for garnet-based solid-state lithium batteries

Abstract

Garnet-type solid-state electrolytes (SSEs) show great potential because of high ionic conductivity and steadiness against metallic Li. However, the unstable property of garnet in air and poor interface contact with Li metal dramatically influence the electrochemical performance. In this manuscript, TiO2 gel is coated on the surface of Li6.75La3Zr1.75Ta0.25O12 (LLZTO) pellets by a spin coating process, to remove the surface impurity and in-situ construct an air-stable and lithiophilic LixTiyOz (LTO) layer on the garnet electrolyte surface. The LTO interface layer can enhance interface contact, improve ionic transport and suppress Li dendrite growth. The low interfacial resistance (18.40 Ω cm2) in Li|LTO@LLZTO|Li symmetric cells manifests good wettability. Density functional theory (DFT) calculation results indicate that the modification layer owns higher work of adhesion and interfacial energy, suggesting excellent stability and inhibition in Li dendrite growth. Specifically, the Li symmetric cells with LTO-modified electrolyte show an enhanced critical current density of 0.9 mA cm−2 and outstanding capability to survive long cycling over 5000 h at 0.1 mA cm−2. The assembled LiFePO4-based full cell displays both high reversible capacity and cycling capability. This work provides a promising strategy to take advantage of interfacial Li2CO3 impurities on the garnet electrolytes.