Facile Li-ion transport in microstructurally engineered hybrid LLZO electrolyte for application in pseudo-solid state lithium metal batteries

Abstract

The present study probes the effects of microstructurally engineered Ga-LLZO (Li6.25La3Ga0.25Zr2O12) infused with solvated ionic liquid (SIL) as an advanced solid-state hybrid electrolyte (SHE) for application in pseudo-solid state lithium metal batteries (SSLMBs). To obtain unique microstructure, gel impregnated based cellulose exo-templating process (LLZOCET) designed and the product powder was duly characterized by XRD, RAMAN, FTIR, FESEM and TEM. The electrical properties of engineered Ga-LLZO demonstrated a two-fold reduction in grain boundary resistance and improved lithium-ion transport at RT with lower activation energy (Ea = 0.37 eV) compared to conventionally prepared Ga-LLZO (Ea = 0.59 eV) by gel combustion method (LLZOGC). SHE was prepared using sintered Ga-LLZO pellets infused with solvated ionic liquid (SIL). The presence of SIL was found to enhance lithium metal wettability at the electrolyte-anode interface facilitating Li-ion transport. The impedance spectroscopy (EIS) revealed 3D interconnected morphology in LLZOCET electrolyte which offered lowered impedance, higher lithium ionic conductivity (0.215 mS/cm) and lowered electronic conductivity (7.59×10−8 S/cm) at RT compared to LLZOGC. The developed SHE showed stable lithium platting/stripping behaviour for >1350 h without dendritic penetration with critical current density (CCD) of 700 µA/cm2;which was higher than conventional prepared Ga-LLZO (400 µA/cm2). The electrochemical performance was tested in full cells using LiMn2O4 cathode and Li metal as anode and cycled (>500 cycles) at different current densities (0.1–3.0 mA/cm2). At 1C, engineered LLZO demonstrated 94% capacity retention with >98% columbic efficiency. The post-electrochemical analysis revealed no change in cubic phase or morphological degradation even after prolonged cycling. The compiled data thus clearly established that engineering at the microstructural level might be one of the critical steps for the realization of workable SSLMBs.