Crack-Free Single-Crystalline LiNiO2 for High Energy Density All-Solid-State Batteries

Abstract

Single-crystalline layered oxide (LiNi1-x-yMnxCoyO2) cathodes have been found to exhibit exceptional electrochemical properties when coupled with various inorganic solid electrolytes (ISEs) in all-solid-state batteries (ASSBs). Their advantages stem from the robust morphological integrity with the absence of grain boundaries and the high electrochemical oxidative stability. Here, ASSBs featuring single-crystalline LiNiO2 (LNO) with the highest Ni content are reported, offering a high theoretical specific capacity of 275 mAh g(-1) alongside a high average discharge voltage (3.7 V vs Li+/Li). Through a careful investigation, it is demonstrated that micron-sized single-crystalline LNO (mu SC-LNO) composite cathodes with a halide ISE exhibit a high initial discharge capacity of 205 mAh g(-1) with an outstanding cycle performance over 200 cycles in room-temperature ASSBs. The significance of engineering parameters is emphasized, such as particle size and specific density, in promoting a homogeneous and fast Li+ transport within the composite cathodes. Furthermore, the formation of undesirable interphase between the halide ISE in the cathode and sulfide ISE separator is elucidated, which may be a critical factor impeding long-term cyclability of ASSBs. This work provides insights into the design of composite cathodes for high-energy-density ASSBs.