Co-sintering a cathode material and garnet electrolyte to develop a bulk-type solid-state Li metal battery with wide electrochemical windows

Abstract

Co-sintering a cathode material and the Li₇La₃Zr₂O₁₂ (LLZ) electrolyte can assist in fabricating bulk-type all-solid-state batteries (ASSBs). However, owing to the use of low temperatures to prevent reactions between the different materials, this process can result in low relative densities and ionic conductivities. To overcome this trade-off between sintering temperature and electrochemical performance, a highly sinterable Ca–Sb-doped LLZ electrolyte integrated with the sintering aids Li₇SbO₆ and Li₃BO₃ was developed in this study. A composite powder of Li_6.5(La_2.925Ca_0.075)(Zr_1.425Sb_0.575)O₁₂ (denoted as LLZ-CaSb) and xLi₇SbO₆ (x = 0–0.14), whose composition differed from that of stoichiometric LLZ-CaSb, was prepared, with Li₃BO₃ added prior to sintering. The disk incorporated with the sintering aid 0.08Li₇SbO₆ (x = 0.08) and then sintered at 750 °C exhibited a relative density and ionic conductivity of 87% and 3.1 × 10⁻⁴ S cm⁻¹, respectively, indicating its superior sintering properties. The formation of a low-melting-point liquid phase, generated by the mutual reaction between Li–Sb–O- and Li–B–O-type oxides, promoted sintering. The developed electrolyte exhibited a wide potential window (5 V vs. Li/Li⁺). The ASSB assembled using the co-sintered LiCoO₂/electrolyte system and Li metal anode maintained 98.6% of the initial discharge capacity (120.7 mA h g⁻¹) after 60 cycles at 25 °C and 0.1C and performed adequately over a wide temperature range (−25 to 120 °C). The method reported herein has potential for achieving cost-effective large-scale ASSB production.