Engineered Li7La3Zr2O12 (LLZO) for Pseudo-Solid-State Lithium Metal Batteries (SSLMBs): Tailor-Made Synthesis, Evolution of the Microstructure, Suppression of Dendritic Growth, and Enhanced Electrochemical Performance

Morphologically engineered Li7La3Zr2O12 (LLZO) impregnated with a common solvated ionic liquid (SIL) can greatly influence the cycling performance (360 cycles), coulombic efficiency (>99%), and high rate capability (0.05–1.2 mA·cm–2) of pseudo-solid-state lithium metal batteries (SSLMBs). In this report, to obtain a unique microstructure of cubic-LLZO, a fine-tuned combustion synthesis process was first designed; synthetic parameters were duly optimized, and powders were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), 1H NMR, and Raman spectroscopy. An in-depth analysis of powder properties and electrochemical behavior of the fabricated SSLM cells revealed that impurities present in LLZO significantly facilitated electrochemical cell performances. Such a combination of the engineered LLZO impregnated with the SIL enabled the plating and stripping cycles in Li symmetric cells with up to 200 h of operation at a constant current density of 0.05 mA·cm–2 avoiding short circuit. The critical current density (CCD) was found to be 450 μA cm–2, which is significantly higher than the other reported CCD values for pristine LLZO. The post-electrochemical study revealed that transgranular lithium dendritic growth, a genuine problem in SSLMBs, was impeded to a significant extent by the engineered LLZO and an in situ formed phase, Li0.5Al0.5La2O4, at grain boundaries during cycling. The multicathode compatibility tests as performed (Li/LLZO-SIL/LMO, Li/LLZO-SIL/LFP, and Li/LLZO-SIL/NMC111) exhibited that morphologically altered LLZO with the SIL interface is compatible with most of the commercial cathodes. The study thus envisaged that the engineered LLZO solid electrolyte impregnated with the SIL can exert a synergistic effect to enhance faster Li-ion conduction as well as resistance to Li dendritic growth, providing a path for developing high-performance SSLMBs.