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

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 Li6.5(La2.925Ca0.075)(Zr1.425Sb0.575)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.